I think there are several main reasons for thread breakage.
1. cheap thread
2. jerky moving in FMQ
3. wrong settings for tension and feed.
4. machine not adequately cleaned and/or oiled
5. Burr on needle, bobbin case or pressure foot.
6. Old needle
7. It wants the day off for no apparent reason.
I know I have had to deal with all of these more than once.