This phenomena is sometimes called the "sophomore slump" [1] in some creative industries and "second-system effect" [2] in software development. To add to your excellent list of reasons why this happens, I'd also add that early success may be the result of spending much more time on the first creative effort than subsequent ones. Some musicians spend years making their first album but then have only a year or two to try to repeat the success for a second album, especially if a label wants them to release another album while they are riding high and before their fame fades (supposedly). Second-system effect refers more specifically to feature creep in second projects in a series, but you can imagine the same thinking applying to creative industries too.

[1] https://en.wikipedia.org/wiki/Sophomore_slump

[2] https://en.wikipedia.org/wiki/Second-system_effect