I like the feeling of a clean app that doesn’t have any ad integration at all.

If I remember correctly pro came out before IAP was a thing.

The in-app purchases can be buggy with amnesia hitting them once a while, making you install/reinstall just so google remembers you purchased pro. This happens when you have more than 1 google accounts on android.

Another reason may have been due to the in app purchase stuffing up sometimes. I believe it was a Google thing, but iirc sometimes it would just forget you’d bought pro within the app and start showing ads again.

Other than the already mentioned points, the old Sync Pro and Sync Dev didn’t include the ad libraries in the app. Sync Dev was on beta track by default IIRC and had an internal test group like the current 100 limited users testing group Sync for Lemmy has.