Diesel is not the same as a gas generator. There are a lot of things to go wrong with gas engines tbh. Diesel on the other hand will mostly run without too much fuss so long as there is compression and there is fuel.
TLDR Diesel generators where you might be without mains for a while and intend to replenish the fuel with deliveries during the outage, fossil gas for use cases where gas delivery pipelines are available (urban, suburban), propane for offgrid use cases (rural, cell towers, etc) where fuel longevity is a concern.