The way I understand it those clauses are written to prevent the kind of situation where you have a problem at work, can't solve it, go home, solve it, then offer to license it to your employer the following day for a reasonable charge.
And if an employ doesn't do any work at work and just does this sort of thing: fire them, then hire them as a consultant. The business just lost most of the tax burden of supporting an employee, e.g. pay roll taxes, insurance, etc. And the employee just got even more intensives to work the way they were before.
I really don't get Americans. Capitalism is good everywhere, but not in the workplace where we need to treat everyone like the dirty peasant they are.
I think the real problem is if the company was sharing in the profits of the invention, and companies took care of workers as they did back in the day, this would not be nearly the point of contention it is.
My father's company pays you for getting a patent, then pays you a percentage for their profits related to that patent, I dont know how they do the math, and it is likely favorable, but the rub is that there is tangible benefits to you for inventing things, oh wow!
When someone invests in your creativity, they are entitled to the agreed returns. You are free to find funding on other terms elsewhere.