One of Diaspora's original developers sadly took his own life in 2011 just when the platform was really taking off. This was a huge blow, and (as far as I can tell) the project never really recovered from the tragedy. The other original developers eventually moved onto other projects, and handed Diaspora over to the community.
Diaspora's current development team doesn't want to use the ActivityPub standard, which almost all other Fediverse users are on. This means there is no way for Diaspora users to talk to Fedi users on Mastodon, PixelFed, PeerTube etc etc etc.
Diaspora's development seems to have almost dried up, and the number of active users on the Diaspora network today is only a few thousand.
It's a very sad situation π and it's a major loss for the wider Fediverse.