Same but I'm pretty sure it's coz they were on different networks which made the crossovers (almost) impossible

^^ Yep That.

And also originally they weren’t even gonna mention Buffy at all in Angel but Ofc that went down the drain in the first 10 minutes lol

It’s actually because of owning rites

There were a few. Last episode of season seven of buffy, angel and faith came. Willow came to help restore angel's soul during season four of angel. Buffy also came into angel for the two episodes of angel.