Some might. But if I'm some ambitious new publisher looking at publishing my setting, it's hard not to dream about making that $100,000 Kickstarter and publishing a nice hardcopy that's not lost among the PDFs. If you're dreaming for the sky, why start with chains binding you to the ground?
Well, yeah. Why would you? Maybe because you're not going to hit the sky by tying up to a supermarket balloon. But more importantly, why should WotC care? How much effort should WotC go to to help out a niche of a niche of a niche? (might be a few more niches in there). Obviously it's great for this wannabe if WotC goes with the OGL. That's dead apparent. But the wannabes aren't writing the license. WotC is. And if WotC can give up say 15% "control"* and satisfy 95% of their consumers, I don't think they'd worry about the 5% that would be happier if WotC gave up 30%.
*I'm using control as a shorthand for whatever it is that is someone thinks WotC might be relinquishing with a license.
I don't think amateur is really relevant.
Well, we're going to disagree there.
I don't think there's a huge audience for low-pro stuff, and I doubt what there is is really something WotC wants. Amateur hour is easy, but I think most anyone that puts some polish into their product is going to dream of hitting it big, so why tie yourself to someone who doesn't want to let you when you can use Pathfinder or Labyrinth Lords or both?
I'd consider "low-pro" to be a one-or-two person company that didn't or can't get products on brick-and-mortar store shelves. There are maybe a handful of companies that _won't_, but there's a lot that can't. That doesn't mean they're not professional, but they're not big leagues. I think that's a hugely relevant group of publishers. Without them, you're talking fan creations or established publishers. I also disagree that putting some polish on a product is a sign that you want to "hit it big".
As to whether or not WotC wants an amateur/low-pro ecosystem, I think they do. Satisfies the need for diversity and customization of the game without getting into WotC's line of sight. The majority of it will remained tethered to D&D and the stuff that isn't won't be very visible, ie any d20-based superhero ruleset vs Mutants and Masterminds.
As to why someone would do it...well, there is no license and Frog God Games is already planning three books. Why would they do that? Obviously for the audience.
All that aside, though, if you think fan work is inevitable and WotC doesn't really want low-pro publishers, the OGL makes even less sense. Who would it be for? Established professional publishing companies? People hoping to vault directly from amateur to Monte Cook status? That's an incredibly small field, and a lot of work for WotC to go through to make them happy for no clear return.
I would absolutely dance with joy and happiness if WotC put 5e under the OGL just like 3e. I would probably sing. I am totally for it. That doesn't mean I think it's going to happen.
Edit: Also, no matter how many benefits of the OGL we point out, there is one absolutely inescapable fact. WotC ditched it for 4e. They saw something they didn't like in the OGL, and went with the GSL instead. You can point to Paizo as the poster child for an OGL system (not that they have a choice), but most people panning 4e are panning the system, not the license (not that the license didn't suck lemons, but...). I've yet to see a convincing argument that the OGL would have made 4e a better and more accepted game.
