1. Is data encrypted in transit?

2. Can the user access their data at rest?

Those two things are entirely orthogonal.

I don't think you can extrapolate a trend from a few apps having bugs in their export code. Google Takeout is also notoriously buggy and they don't use E2E encryption. A more likely explanation is companies of all kinds don't care that much about export functionality, due to the incentives involved.

you CAN extrapolate from nearly all e2e encrypted apps not giving a way to use the data. And there is a big difference between buggy google export features or facebook actively making export unusable to lock in users.