I think the four biggest drivers here (nothing mind blowing) are:
Expenses- Necessary expenses like rent, food, utilities etc. If this is a higher % of overall budget saving is hard.
Income-Probably more obvious then expenses but similar mindset. The less you make the harder it is to save.
Behavior-Probably underrated. I see most things falling into needs, wants and desires. We need to eat-$4/meal, we want Chipotle-$10/meal and we desire the steakhouse at $40/meal. Too many people get this wrong not only with food but other things like autos, houses, clothes etc.
Time allocation-kinda ties income income. The way that people spend their discretionary time is critical. If you don't have money maybe Ubering, Instacarting or other second jobs are better uses of time than going to a bar and watching rich athletes do their job.