It was definitely the fact it was Windows-first, IIS-first and smelled of Enterprise Software (i.e. Not Cool(tm).) mono was workable but second tier, though I feel it did help convince MS that the dotnet project is worth pursuing.

Today I'm running a home asisstant with a side service written in dotnet on a raspberry pi 4 raspbian in docker containers. If it didn't advertise the dotnet version in the logs I'd never know.