That does tend to happen a lot in comics. It's called "attrition."
Not every comic it happens to is viewed as a "failure." Comics tend to run their natural course with a relatively small percentage being break out hits.
It's also the only one that doesn't feature either Peter or a traditionally heroic Spider character, like Miles or Gwen.
Editorial can initiate a story arc or introduce a character. It can't dictate how readers respond. Readers responded very well to SSM. They don't have to be interested in seeing Otto's heroic journey continue for years to come in order to make the success of SSM considered valid. Ben Reilly can't support widespread reader interest either but that doesn't mean that the character didn't win over a devoted fanbase during his time.
When someone's success eats away at you so much - as Slott's clearly does you - that you need to dismiss, diminish, or explain away that success in order to make yourself feel better it speaks volumes.