Originally Posted by
PeterParkerSpider-Man
Because some people like the original thing they like, and don't have to like change? People didn't want to see Shia Labeouf take over as Indiana Jones, either.
Yeah, there are back issues of Spider-Man to read, but would you like it if someone said, "why do we need new tales with Miles? There are years of issues you can go back and re-read." People can read the old stuff, but they want new stuff, too.
There's a big difference between "change" and "completely different," as well. "Change" would be having Peter Parker get married, or giving Peter Parker a symbiote costume. Change is Peter and Jonah becoming step-brothers. Change is Peter Parker working at Horizon labs. "Completely different" is someone else under the costume and calling themselves "Spider-Man."
I don't need everything to be exactly the same 100% of the time, but I do require there be the "essentials" for me to continue reading. One of those essentials is Peter Parker. Peter is the one I grew up reading, he's the one I'm invested in and attached to, he's the one who means more to me than any other fictional character, ever. So I don't appreciate it when Marvel may possibly take him away, put someone else in his place, and say, "He's Spider-Man now. Don't like it? Too bad."
To answer the thread title, no, Miles shouldn't replace Peter. Become his own Spider-Man? Sure. Become the Spider-Man? No.
Give me a book with Peter, as Spider-Man, and I'm a happy customer. I'll check out Miles, too. But I don't read replacements for my favorite characters, because they're irreplaceable to me. I stopped reading Ultimate Spider-Man because Ultimate Miles was a replacement for Ultimate Peter.
If Miles is his own thing, and Peter-Spidey is his own thing, they'll have my money for both books. But if Miles is a replacement = no sale.