@kirby St. Terry said he was trying to recreate the C64.

Back then, people had a computer, and you'd order magazines, the magazines would have these 1-2 page programs in them: you play a game by typing the game in from the BASIC program in the magazine. People would sit and type the program in from the magazine. It is nice to be able to download a program, but you can see how that loses something slightly. If you have typed it in yourself, then you can see sort of how things work, and if you make a mistake when transcribing it, then you can reason about what does what (if you use X instead of Y, then this thing happens), or you can see how to change things. I didn't have that kind of thing around when I was a kid, but I can see that, I think people can see that.

So St. Terry didn't want to add a TCP stack, this makes a lot of sense in that context.