Disney is an all around really solid company that has an amazingly good ratio when it comes to quality movies, even if it's not films that are your cup of tea. And it's less about monopolizing everything and more so just a case of Disney wanted to try to get away from being seen as something mainly for girls. They're purchase of Marvel was specifically to get a huge pie when it comes to the boy market.
Lucas selling Star Wars to Disney felt more than natural, he's had a fantastic relationship with Disney for years, to the point of licensing rides for both Star Wars and Indiana Jones for the Disney parks even while the franchises were released by other companies.
The acquisition of Indy was only a matter of time, when Paramount's deal went up.
I look forward to what Disney does with the fifth film.