Well, that would just shift the problem: Now, instead of wealthy people being less deterred, it's the people with a bunch of free time that are less deterred (college kids screwing around, people with no job)...

Also, it doesnt benefit the society any more that the fine's money would (assumuning the community service would be equivalent to the current monetary value). (There are also other problems like verifying the work is actually done and also small fines, like, am I supposed to pick up trash from the sidewalk for 2 minutes for jaywalking?)