what everyone already said. I just upgraded commuters from an old MTB beater to a road hybrid. I have much more difficulty riding no hands on my new hybrid. Different geometry, bigger wheels might have something to do with it. I think the narrow seat on my new hybrid also makes it harder for my bum to get a grip on the bike when riding no hands than the gel seat on my MTB.
Put all of your weight on your sit bones and sit up straight.
+1