It’s not just reusing themes from TPM in AOTC and ROTS, it’s reusing the exact same recordings. Over and over again. A lot of this had to do with Williams’s busy schedule in 02 and 05 but most of it had to do with GL’s last minute editing changes.
TPM is a truly fantastic score, though I will say I do believe I prefer a score like TFA more because, when you get down to it, JW’s working off what he has to work with. So I’ve always thought “Anakin’s Theme” was a terribly boring bit of music and really don’t care for its use throughout the score. But of course that’s because of the character Williams was writing for. I also am of two minds on Duel of the Fates. Is it an amazing piece of music? Absolutely. Is it also ridiculously over the top? Yes. Why do we need an epic choir for that lightsaber duel? Why do we even care? Well the answer is we don’t, and thus JW is compensating and trying to make us care with his awesome music. But there’s still a dissonance there.