They wanted to make it different to sell it better, and they also came up with the idea of changing it into simon's 3rd adventure by changing the prologue into something completely different.
I don't remember the English prologue setting it after Simon's Quest, I thought it still set it at the same time as the nes one. Granted I haven't played the English one in awhile cuz I like the unaltered original better, the green blood looks horrible.
People were more likely going to buy it if it's the continuation of Simon's saga rather than the same game with prettier graphics.
I see what you're saying but a lot of super nes games did that, they'd just remake/update the graphics to a game and call it super "X". I think the raw power of the super nes sold games just like new elements, innovative ideas and sequels to classic nes games did. People wanted to play updated versions of their classic nes games and were willing to pay big bucks to do so, like with Mario Collection/All-Stars on the SNES.
It is also not the same game. most levels are completely different including the final boss battle.
I know bro, I was telling him to skip over it primarily because of the price, but there is fun there, just not nearly as much as with Rondo and the frustration level on the last fight ranks up there.