(Note, that currently its taking its own toll on their development. As they've to (manually) keep up with FPC updates. It would be so much easier, if FPC was using git. So much easier to use and NOT to share. Must switch to git, asap!)
There's an existing Github mirror of FPC that's automatically updated constantly, at least.
Why should they bother? Simply placing a download link on a site, is already an expensive thing.
One has to pay a webmaster money to update the site... and then maintain it.
It's more a question of "why doesn't Blaise Thorne, who they paid to develop it, just have a normal repository of it literally anywhere of his choosing."
(Bitbucket, Github, Gitlab, e.t.c., wherever, doesn't matter at all. Plenty of free options out there.)