Short answer they got greedy.

Long answer they started making modpacks they call collections which isn't bad on the surface but in order to stop them from breaking they removed the ability for authors to delete their own mods. Which doesnct look good but even versions 'removed' are still accesible to the API to download them. But free users have to manually visit pages to download the mods. Paid users skip that step rendering them the only one's able to get those archived versions, and also robbing the mod authors of potential donations from page visitors.

Suffice to say they looked at Bethesda, and said we can even screw up better. Great Success!