Instead of coming up with conspiracy theories we could consider what other options there are. There are effectively only three powers which could control Gaza if/when Hamas is defeat: Egypt, Israel and the PA.
Egypt certainly doesen't want anything to do with the region or Palestinians anymore. So US can only chose between supporting a direct Israeli occupation or a semi-indirect one (through the Palestinian Authority). I don't think the US government wants to install a puppet regime in Gaza, they'd rather have absolutely nothing to do with at all.
Tangential but when it comes to Afghanistan I'm almost certain that stupidity and incompetence (and one might guess a good dose of corruption) rather than outright malice or imperialism were to blame for that entire disaster.
> Palestinians real autonomy
Well to some extent Hamas was the closest they got to that for decades.