Here’s my guess.

1. Tumblr users as a demographic are closer to fedi users than the Facebook/Instagram masses.
2. There just aren’t that many Tumblr users anymore, at least compared to the overwhelming horde that is Threads. The threat of diluting the culture is just a lot lower.

imo Tumblr has always been the ‘weird kid’ of social media. in the past it definitely stuck out as unique and nowadays even though they’ve tried to act more like xitter and Instagram or whatever the users tend to be vehemently against the changes

Saying Tumblr is corporate in nature is like saying the lord of the flies Island was democratic. If they so much as changes a rounded corner to be sharp or vice versa the entire site throws a shit fit.

WordPress is open source, for one.

I would say yes? They make Wordpress which is pretty open and usable by default and it is properly opensource. Since taking over Tumblr they seem to have been making reasonable improvements and in general trying to keep it open.

In general they have been favourable to open source and open standards. So when they say they are adopting an additional open standard I have high hopes.

But FWIW I also think that Threads joining the fediverse is likely a good thing. It is true that it may allow many people to be more comfortable on a user-hostile platform, but IMHO that is their right. I think the biggest concern is that if Threads or a small number of large platforms are the majority of users they can add proprietary extensions but I don’t think the biggest issue. The biggest strength is making the fediverse more popular, and allowing more people to pick more open options without needing to ditch or convince their friends upfront.

Those of us that are still using Tumblr are very against data collection and adds, Automattic has made some mistakes and us users are not very happy with them so they know they are on thin ice