Was the only motivating factor money? I just can't put myself in the mindset of a Greek farmer during 40BCE and agreeing to fight for some random guy that just appeared in my home town.
Why would I fight for this guy? Why risk my life?
Were generals promising un-rejectable amounts of money? Maybe the chance of actually dying during battle isn't that high, but it's still a risk. I know that a lot of the time battles would end in retreat/defection so it's not like they're fighting based off loyalty to the empire. Was it primarily mercenaries, or locals that generals were recruiting?
More can be said but u/iguana_on_a_stick has a big answer here in general about Roman manpower and how the army changed throughout the Republic into the Empire including a big section on motivations.
https://www.reddit.com/r/AskHistorians/comments/fgxsty/why_was_the_late_roman_army_so_much_worse_at/
Also you may be overestimating the quality of life for many, if not most, farmers. A promise of steady pay and food might seem pretty nice if you're a bad harvest or two away from starving to death.