This is a strange thing to believe - fines exist for deterrence, not income - the purpose of a fine has failed if it ends up being paid, since it didn't deter the offender!

In the UK, for example, about GBP 80 million in speeding fines are issued each year. The annual police budget is GBP 12.5 billion though, so fines are a tiny 0.64% of that, hardly significant. Having said that, it looks like the road policing budget for 2018-19 is down by a large amount, from the GBP 200 million in 2016, to about GBP 90 million, so the fines would seem to cover most of that... Not sure what to make of that, now?