Skill development, in the model of K. Anders Ericsson, requires a certain type of deliberate practice, not simply "hours of practice." Moreover, he argues that it's only possible to spend a few hours a day at deliberate practice. The rest doesn't contribute to improved learning.
After a few real years, you'll start to appreciate how much experience your brain gets when you're washing the dishes. You need time away from the primary task to get better at it. I also echo the other points.