What made you choose mtb?

I realize a lot of people grew up with it or came from bmx , I’m more asking the people that got into it later on.

I’m mostly just looking at mtb as another means of fitness to supplement my running.

I’m not sure if I want to get a mtb or gravel bike. I like the idea of being able to get a really good workout in an hour or less ( everyone that gravel or road bikes seems like it’s real long sessions due to being easier) but I also don’t want to jack myself up lol. Though I guess nothing says I have to ride anything crazy and can walk the bike if I need to. Also could use the mtb as a gravel bike if I want.