Wild speculation here obviously, but it could be a regulation play--there's a lot of potential legislation that would regulate what you can legally 3D print, which would warrant a system to be the age-verification equivalent for 3D printing.
This is admittedly a bit tinfoil hat, but they wouldn't be the first company to attempt to legislate away the competition.
They are also subsidized by the Chinese government and are paying for users exclusively hosting on MakerWorld. Their move is obviously complete market capture, not sustainable finances at this point.
There is a lot of things going on. We can only speculate, but it sure ain't going to benefit end users.