Cars that you just could not get insurance on.

So I'm trying to sell my Range Rover Classic and a guy locally offered me a Daihatsu Esse as Part Ex. Went on compare the market with the reg for an insurance quote to see how it would match up. No luck. Called a few people like Adrian Flux who for whatever reason "Could not offer me a price at this time" Seems a bit random but okay. But it did get me wondering has anyone else had something like this and what was the offending car?