Do you not understand why PR isn't a state? Seems like you don't. Support for PR statehood is only about 50% (on the island). That largely has to do with the fact that their taxes would increase if they became a state. Additionally, they would have to switch to English (along with Spanish) which makes things a lot more complicated. They are already US citizens and can move to anywhere in the US if they want to vote in federal elections (and half of them do but mainly for work). They don't want independence either. So the current limbo state is actually desirable to them.

Even if the citizens of PR wanted statehood, you have to get both parties to agree. This means probably 2 states at the same time (one red, one blue). Since there isn't another potentially red state (Alberta but that's probably never going to happen) to join, that's hard to do. Look at US history, statehood has always worked this way. It has nothing to do with whatever you are implying.

PS The 27th amendment was 1992, probably during your lifetime. You would expect the rate of new amendments to slow overtime so the average of a new amendment about every 15-20 years seems about right.