Sure there are unskilled workers who mow, trim. blow and go. I see them all the time. One homeowners lawn service put down mulch in the early fall and within a month the beds were full of leaves. Real skillful! Whoever posted that statement is on this forum for a reason. I wonder why? I would bet the reason is to learn and be the best at what he does.
The skill comes when you keep learning and growing. Besides just mowing, you learn to identify weeds, disease and pests in turfs and ornamentals and know how to treat them. How to lay sod, what times of year to trim shrubs, fertilize etc. etc. Skill comes when you take pride in your job and want to be the best you can be.