Despite delays, the plan to connect Tumblr's blogging site to the wider world of decentralized social media, also known as the "fediverse," is still on,
Tumblr users as a demographic are closer to fedi users than the Facebook/Instagram masses.
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.
Here’s my guess.