With flying, it's all happening at once: Radio is going, three controls, then add flaps once you start taking descents... it's a huge nightmare for practising -- you just can't, you just DO it! Kind of like teaching; first year teachers get thrown in, andyou just GO! You don't start out with only 3 or 4 kids, and build up to 27 -- you have to do it perfectly from the beginning! Except, with teaching, if you mess up, the kids die slowly, and there is often time to save them if they get a better teacher the next year, whereas with flying, if you mess up, you will -- as my flight instructor says -- "have a bad day".
Arrrggghhh!