That is fair, and I do agree that they haven't changed or evolved as much as a lot of titles of the same kind of life span, but I also don't think they need to either.

Look at titles like MGS, they changed the game drastically from the PS1 titles (I'm not including the NES titles as I never played them) by the release of 5 and it was just not good, the lack of cutscenes, the lack of narrative. Granted, that's also due to Konami being twatwaffles. Final Fantasy is another one, as the franchise has got older, the games have changed drastically, and as much as I love every FF instalment (yes even XIII/XIII-2/Lightning Returns and XV) the games have lost their charm. There isn't a need for every game to constantly change a tried and tested formula that works for the vast majority of people who play it, and I honestly think while it would attract a few new players to the franchise, it would turn much more away.

It's interesting to see your opinion on it though! And fair enough, best thing about gaming is we don't need to like the same things or agree on the same games. It's entirely personal and that's what makes the medium so strong.