Because skilled people justifiably cost more and that raises prices that people are unwilling to pay. An example: Back in late 1983 I bought a new-to-me house, and among other minor maintenance things it needed was a new mailbox. So I went up to the old-time established Mom 'n Pop hardware store and looked around for a mailbox and found what I was looking for, a simple mailbox that mounted next to the front door, and it cost $15.
Now, it so happened that a brand new Home Depot had just opened a few blocks away and of course I'd heard of the debate going on even then about the big box stores driving out the small stores and I decided to go have a look. And there on a shelf was the same, identical mailbox. For $7.00.
Can anyone tell me what I'd get (besides maybe a warm fuzzy) for my $8.00 if I'd bought the mailbox at the old-time hardware store? I didn't need or want a skilled tradesman to help me pick out a mailbox and I sure wasn't going to pay for him. And to make the decision even easier I was fresh out of a divorce and had spent just about my last dime on buying that house. I just needed a mailbox and could not afford the luxury of supporting old and inefficient business models because that was the way grandpa did it.
I get that Home Depot buys mailboxes by the trainload and can sell them cheaper than the local hardware store that buys them by the case. It doesn't take an MBA to see the economies of scale in that.
Not surprisingly the small hardware store was gone a month or two later. And so went a piece of local history, and I was $8 better off.