In both cases, there's a limited number of slots available for what's fundamentally a required educational program, and increasing that number of slots is difficult on a structural and staffing level.
There is no set limit like with the match or residencies. New schools can open up, existing schools can increase class size or run additional classes to match demand, and they have the incentives to do so.
The match can do that, too. 2019's had 6% more, because more programs joined in. There's no set limit; there's a limit to how many slots Medicare subsidizes, but programs are free to offer self-funded slots over that.
In both cases, there's a limited number of slots available for what's fundamentally a required educational program, and increasing that number of slots is difficult on a structural and staffing level.