CV axle problems

So, the Volvo fluids and filter change went smoothly. The CV boots... Not so much. After reassembling the car and starting it, it wouldn’t move. The inner cv joint just falls apart.

Here’s a video of the axle out on a bench, inner driver’s side CV joint assembled, able to move and swivel. But pulling it out just breaks it apart, it’s supposed to stay all in one piece, no?

Any ideas? I’ve already set up a deal for a whole new axle, but I still want to figure out what went wrong.