Well what I'm referring to is that the implementations linked in the thread are industrial embedded solutions likely for POS, digital displays, etc. Of course a platform is just a platform; the manufacturer can do what they want with it if there's a big enough need in the market. For the intended purposes, the Realtek NIC is just fine and saves the manufacturer a few bucks. Consider also that these are embedded (i.e. long life deployment) systems. I doubt a manufacturer will risk the Realtek NIC if they were truly that bad (and they're not).
My humble point is that we can't always have what we want. For example I want a NUC/thin-ITX sized platform with an 8th gen Intel CPU with at least 4 Intel i350 NICs to upgrade my PfSense, but alas the products available on the market are nowhere near what I'd like. Most are 4th or 6th gen, with i2xx NICs or even 82583V.
On the topic of Realtek NICs, they have come a long way. Remember that Realtek AC97 audio was roundly pilloried, and even Realtek HDA audio wasn't that great. I was pleasantly surprised in my last workstation build that the high end Realtek HDA solutions are plenty adequate, certainly to my audiophile ears. Sure certain discrete sound cards are "better," but are they "$100-200 better?" The main problem I saw with past Realtek NICs 10-15 years ago was the driver first and the hardware second. For the most part the hardware portion has been fixed, and Realtek seems to be a bit more proactive with providing or helping Linux/BSD developers with the drivers. Sure it's not to the level of Intel's historic NIX support, but in my view, completely adequate for the intended uses.