Bone and joint health. Legs have evolved for impact and weight-bearing, they need it to remain healthy. The optimum dose is unique to the individual. Too little is easier to achieve than too much, for most people.
Keywords: osteopoenia, sarcopaenia, balance.
It’s a good question and the poor answer is: Nothing is counting my cycling.
Yeah it's a bit of a gap in the most popular wearables, I feel. Many can do it, but the pedometer function is typically automatic or "always on" while cycling tracking requires some fiddling. Some Garmin wearables (and others I'm sure) can do "smart" activity recognition, automatically determining if you're walking, cycling, lifting weights, etc. with variable accuracy.