why do some cassette decks eat tape out of cassettes over 90 min?

Here ya go!
TAPE THICKNESS

Did you know that the longer the tape length (90 and 120 minutes) the thinner the actual tape? It makes sense if you think about it, after all they had to make it fit within the tape deck, but the thinner the tape, the more susceptible to breaking.

Hungry

@yogiboy thanks! makes sense.

Although it has been a while since I used my cassette deck, I do recall that if the capstan, pinch rollers and heads are not kept clean the tape can sometimes stick and cause mis feed.

If the torque of the takeup spindle is insufficient, the machine will eat tapes. This first shows up on longer cassettes, but if unattended, will eventually manifest on any tape. The usual culprit is a perished tire on the takeup spindle itself. Sometimes there is a belt involved too. Any cassette machine is old enough at this point that if there is a problem like this, all the rubber bits in the transport should be replaced.