Um yes of course it will cost some but that doesn't mean you have to do work you don't want to do. Over the past 23 years or so and 10 in business for myself I can tell you about half do not want us to do their clean ups. So when I have a list of 190 lawns I know I will have 80-110 clean ups.
The trouble with not doing the clean ups is guy like myself will not take the clean up. I gave that up year 1 I have a short window to work in and it wouldn't be right for an existing lawn client not to get done because we got snowed out because I did a day or 2 of one timers.
But that doesn't mean you can not find mow only lawns. There plenty out there and the new developments tend to have the lower % of clean ups since they typically have few or no mature trees. The older neighborhoods it's a little harder to avoid the clean up end of the trade.