So here is the thing: only a small minority of TV users are streaming 4K video files over their home network. The lion's share of TV users are streaming from apps, where the bandwidth requirement is significantly lower. That's why there's only 10/100 ethernet ports. From the manufacturers perspective, there is no reason to put in a gigabit port, because most users will never actually need that additional speed for what they're doing.

This is not going to change until we can start streaming from apps above 100 MBPS.

There are streams that can exceed 100mbit/sec but people are forgetting if TV can decode those or not. Most cheap smart tvs can't decode such streams so it doesnt matter.

We have fiber at our new home (500/500). I have a Hisense Android TV in the Living Room, an older Sony TV connected to a Google TV with Chromecast in the Master bedroom, and a TiVo Stream 4K closest to the router. I literally just had to buy a USB-C to Ethernet adapter for the Google TV and move the Hisense TV to Ethernet over Powerline too.

Fun fact: Even the official Chromecast with Google TV Ethernet Adapter is only 10/100, not Gigabit. Like your TCL, the Hisense TV also hides this spec by just saying "Ethernet: Yes" lol. While wirelessly they both test "faster" over 100Mbps, we have some odd interference from either the walls or neighbors that causes dropouts in the evening where the Hisense and Google TV are located. Doesn't impact the TiVo closer to the router, so that sticks on WiFi, but while both test below 100Mbps on a speed test (more than enough for 4K) no more dropouts and things play smoothly all.the time now.

I think the OEMs don't want to spend this money on a Gigabit port, because 100Mbps is already more than adequate for 4K content and assume most people live in some kind of perfect Faraday box with no neighbors and within 10 inches of their router.

A. Yup. When even Google won't spend the extra money for a Gigabit port, don't expect other OEMs to.

B. Probably because most people don't care about Ethernet at all or they don't want to show they cheaped out on a spec when price shopping (HDTV profit margins are incredibly thin).

C.  ¯\ (ツ) /¯ Sounds like they didn't know themselves and assume everyone has perfect Wifi networks; why would you ever want to use a CABLE -TCL rep probably

(And if so, what reason is there for this in 2021 on TVs advertised as 4K)

Because it's cheaper, and people want "wireless" so they put AC wireless in them instead.

(And if so, what reason is there for this in 2021 on TVs advertised as 4K)

100 Megabit is definitely 4K capable.

YouTube @ 4K60 is ~25 Mbps

Disney Plus @ 4K HDR is ~16 Mbps, Peaking at 30 Mbps Source

So, yes it sucks that it's not Gigabit, and I definitely think you should have Gigabit by default these days, but 4K content shouldn't be a problem being carried over to your TV.

However, if you do experience network lag during 4K video playback: I would blame it on the CPU that your TV came for not being able to handle the maximum bandwidth of the Ethernet port.

Not all but most, same with the TV boxes. Just to cut costs I guess.

Personally I'd just buy a new box with one, built in always sucks IMO.

It’s an oversight but the 95% of people have or use wireless . AC spec is standard now and even n on 5ghz is almost gig in ideal. Better off to add a repeater if you need higher speeds . There are some USB adapters that will use usb2 to bring you up to about 400 with a fire stick or googleTV .

i was kind of surprised when i saw that my new Hisense H8G was only connected at 100mbps when wired to my router (i moved into a tiny studio apartment, everything is right next to each other, figured i'd just use a wire).

but i don't think it really matters all that much, 100mbps is way more than enough for 4K/HDR from Netflix and the like and so good enough for the vast majority of users. if you need something more, a game console or dedicated hardware device is easy enough to use. and, of course, there's always WiFi and every newish TV is going to have WiFi 5 or 6

Thanks everyone for some great answers. I definitely have learned some stuff I didn't know (and also now have brand new questions as far as troubleshooting some things).

I do find it interesting that no one has even addressed the other part of this, which is... why are these specs buried? What troubles me is that other people are going through this frustrating process because everyone tells them (including the TV manufacturer websites!) "If you're having issues with wifi, use Ethernet." If the old standard of "wired is always going to be better than wireless" isn't true anymore, the FAQs need to be rewritten.

I can't think of any other computer-based device I've owned in 25 years of owning computer-based devices where the actual specs on the components can't be easily found. It took me days to find someone who just knew the answer. Every single person I talked to from nonexpert to very expert said, "It makes no sense that wifi would get you better speeds than wireless, there must be something wrong." I spent money on new Ethernet cable and hours taking to TCL customer support, who either were not knowledgeable or were deliberately obfuscatory, and all of that could have been avoided if somewhere this detail was written down or someone at TCL knew what they were doing. It's just very frustrating.

Some 2021 Sony's have 1gig Ethernet. But most only have 100mb links. Wifi is 'faster' in that case.

Weird I have a TCL 50P6US and it connects to the switch behind the TV at gigabit speed.

I don't know about all, but most are only 100 meg ethernet. You will never realistically need more bandwidth than that. Even local media, such as raw Blu-ray rips, are highly unlikely to need more.

What's built into the TV is never going to be the best. They all cut corners on the "smart" part of the TV. Don't worry about what is built-in, and use an external streaming device if needed.