I agree with KeroPower
smell
most hobby shops do not carry model diesel fuel in the US
oil mess
But I think the biggest reason is "monkey see, monkey do", there's not many of us doing diesels. I'm in 2 clubs one club has 40 members the other 140, only one guy had ever seen a diesel run before I brought mine out. I think their time has past, but I love the little stinkers, there is nothing cooler than a tiny diesel.