I think one of the BIG problems is that people GIVE UP on an “SEO project” because it will “take too much time” because they have been given a scary laundry list by an “SEO Expert” and they are unaware that SEO is incremental, and that it can be gradually accomplished, if there is not enough engineering bandwidth.
It may be optimum to roll out everything at once, but it is often not realistic. For some strange reason people may put off a simple fix “because it is part of a larger SEO project” and they don’t get their URLs aging.
To an extent I think this is a product of SEO-mystification, as consultants want to have the biggest project possible.