No specific reason. I used these Gapps on another phone...
You are right. They are 64bit. I totally forgot about the fact, that the old tablet could still have a 32bit ARM CPU
Thanks for the hint, will reflash it again. I was wondering why the animations were a little laggy. But video playback worked without a problem. Weird no application cryed out loud, that it doesn't want to run on the wrong architecture...
Used the mentioned BitGapps after a full wipe. Looks good, no big problems so far (only rotation was stuck once). No bootloops. Maybe I should mention, I don't use a sim card in this old tablet.
Didn't bother to look up the whole bitgapps-config issue, but this could give some good extras like youtube vanced, if needed.