The ultimate answer given later in the above-linked comment is that bootstrapping with FORTH is a great idea but programming in FORTH isn't fun enough to follow up on the notion.

Bootstrapping with forth is a GREAT idea. I think it's one of the best languages to use for bootstrapping.

The reason is simple: forth can be almost the first thing in the chain, and it's so flexible that most of the rest of the bootstrap can be done by simply building up forth definitions.

The way the bootstrap chain generally builds up the level of abstraction is by compiling a somewhat more general language, multiple times, until you reach something usable. If you bootstrap forth you're basically there. You have clean, readable source code that can be ran with a ridiculously simple interpreter/compiler. It's a very natural choice.

But of course forth is such a different paradigm that most people just don't want to learn how to write in it properly (in such a way that you end up with actually readable code). Which is fine. I guess it really isn't fun enough for most. But it's difficult to ignore just how great of a fit it is.