How many of those actors, who insist on doing their own stunts, are doing it because they consciously or subconciously need to compensate for their substandard acting ability?

In Cruise’s case, also because he is short ( 5’7” or so) and has to continuously prove how manly he is.

Also they may simply enjoy the athletic challenge involved.

One other factor to consider is that they get paid for both, acting and doing stunts.
Its also one way to keep fit and sharp.

Hard to guess. I don’t think Chan and Cruise do it for that reason. Not sure about others.