They don't rely as much on unpaid outsiders to run their communities. As in, you're more likely to get banned altogether from Twitter or Facebook by some automated system, while Reddit relies on volunteer moderators so most of the time, bans will be on a per sub basis by those volunteers.

On top of that, afaik, Facebook and Twitter didn't try to spread lies about 3rd party devs using the drama as leverage to blackmail them. I don't recall much about when Facebook did it, but with Twitter, I think Musk was pretty straight with saying that those 3rd party apps cost money to support and he'd rather do it in house.

Finally, Reddit relies on volunteer moderators, but does not (and has for years promised but failed to) offer the associated tools moderators need. So all those are third party things which also end up in doubt with these changes. With the way Reddit have attempted to deny that they want to kill 3rd party apps despite it being obvious, and the lies about devs, I think it'd leave an even more sour taste to everyone if they tried to carve out an exemption for specifically moderation tools, since it'd make it even more apparent what their goal is.