Would you pay $250 to see a movie which took 3 years and $50M to make?
And that's what prices paid GMing out of the market.
Let's take a guy who makes $40K/year at his day job. Which is about $20/hour (dividing by the simple 2000 hours per year metric for quick approximation).
He's looking to change careers, and for practical purposes, needs to make the same amount of money in order to pay his bills (lest he lose his car or house or wife because they're broke).
Let's say he runs an 8 hour game. And pretend it takes 1.5 days to prep one of those 8 hour sessions. For a 5 day work week, that's 2.5 days total per session. (I'm trying to keep the math sort of simple here).
He can run 2 sessions per week (one saturday for Group A, one Sunday for Group B).
So it takes 20 hours total to do a game, 8 to run it, 12 to prep it. That's $400 he needs to charge for that session.
In order to maintain his $20/hour ->$40K/year lifestyle/expense level.
I think most of us would agree that $400 for a D&D session is a lot of money (even split 4 ways for the standard party size is $100). One could argue we'll pay $10-20 for a 2 hour movie, but there's gonna be some serious consumer balking.
So, let's get less greedy. Let's plug in a guy who makes minimum wage ($8/hour because I don't know the current # exactly in the US).
That's $8 * 20 hours = $160 bucks. Would you pay $40/player (assuming standard party size of 4) to play D&D with your friends under a professional GM (in a world where nobody GMs for free, perhaps)?
Sure, compared to a movie, it's a bargain for 8 hours of fun at $5/hour. But people aren't rational about stuff. And they tend to look at the big # without considering the time span. So a movie looks cheaper to most people.
And we're talking about paying a guy minimum wage. That's $16K/year which is like right next to the poverty level.
That may be a dream job to work at, but it don't pay a decent wage (by US costs of living).
Note: the danger in considering the economic value of a product proposition is playing the "hobby" card. In that somebody will do it for less than the work is worth. Sure, it's true, people are GMing for free now (and maybe 2-4 people on the planet get paid for GMing). But that's not how you make an economic determination on whether a proposition is worthy of investment. You look at its dollar cost, and value, compared to alternative activities that make also money. then you look at the final figure and determine if the market will bear that cost. If that answer is no, then you probably don't have a viable product.