Nostalgia sells. That's one of the reasons why there was some money to be made by publishing comics, at least before the pandemic. Marvel may follow suit and reduce the number of publications now (like DC).
As to why keep using a character they're determined to keep dead... same reason, they think they can make a profit.
And yes, I also feel that the idea to bestow powers on virtually every character in the supporting cast, to see what sticks, is idiotic, but for whatever reason, with Spider-Gwen they struck a little bit of gold.
Also yes, sometimes is very easy to be a Marvel writer, you just have to be there and wait your opportunity.
Finally, not all retcons were bad (Blue).