I agree that bachata all sound quite a bit alike: the same instruments, the same rhythms, the same sort of voices. But the lyrics are different and some of the singers are different. It's like rap, with the difference is that rap is deliberately annoying, while bachata is only repetitive, like cumbia and vallenato and sambas.
I find it is more easily endured when one is outside of several cervezas.
Popular music everywhere is tedious, formulaic and repetitive: the rhythms, instruments and voices vary with the country.