Reflecting on how much I enjoyed Shrek2, and on why I enjoyed XMen2 more than Xmen(1) and where Spiderman2 fits into the picture, I believe the prediliction for identically named sequels has grown over my lifetime.
There was never Ben Hur 2. Or Lawrence of Arabia 2.
Things like Star Trek were an oddity. Something for a passionate fanbase that were already used to the concept of an unending serial storyline.
Is it just the mass marketing machine that, having identified they are onto a good thing, milk the populace's desire for more of the same? Or has the viewing audience gotten lazier, avoiding the challenge of entering in the realms of new thoughts and ideas? Or are we now just spending more leisure time on entertainment media, so there is room for old ideas, but we now are also able to take pleasure in revisiting favourites.