Yes! Because if you’re taking payments from users you (should) feel more obligated to keep it online/functional. You’re more likely to shut down a paid relay if you no longer have time/interest in dealing with it or if it’s costing you money. 

People who choose to run free relays have a more set it and forget it mentality. It has tradeoffs but they tend to stick around longer because they aren’t as short term profit/break even motivated.