Only on flat smooth surfaces which are a relatively recent invention.
Take them on any natural environment and it falls very quickly below walking.
I rode my mountain bike A TON as a kid, gave it up for the more "prestigious" road cycling as an adult, but maybe 2 years ago bought a mountain bike to ride with my kids.
My goodness it took about five minutes on a local trail to feel like that same little kid I was back in the day, the feeling of speed, focus, and flow. There's nothing really like it for me, as it puts me square in the moment.
Colombia could have been a better example, they have real mountains and people over there do use bicycles to do their thing. Granted, not a great percentage of the population does it because you do need to be really fit in order to handle 10% slopes, but of those that do you might get future Tour de France winners.