Assad getting overthrown was related to the big geopolitical confrontation with Russia (cold war has never really ended fyi). It was a move against Putin, trying to cut off his ally, as well as secure new pipeline to Europe to damage Russia economically.
Currently Germany, the largest EU economy, is dependent on Russian natural gas. Once you cut that dependency, Russia will get weaker and more isolated, which is in national interest of US I assume. US is also trying to make Germany less dependent on Russia so they can put on more pressure on Russian economy without damaging Germany's economy.
Google is your friend, there were plans for the Iran–Iraq–Syria natural gas pipeline and Putin intervened to stop the project as it was against Russian national interest. Also don't forget about Russian military base in Syria, getting rid of that in the process would be an added bonus from US point of view.
I did not specify business interests exclusively btw. It could be business interests or national interests (or combination of both, often when a country pursues regime change as a part of national interest, there are private companies that make profit).
Governments do not get toppled only for economical benefit, often it's mainly because of geopolitics, see cold war, both US and Russia were toppling over governments and installing puppet regimes in various countries as part of their fight for dominance. Economic/business interests are secondary most of the time.
Reasons for overthrowing Gaddafi were iffy at best also (I'd would actually like to turn the table and let you explain it to me, because I haven't heard any valid reason why we randomly started bombing Syria).
I'm not familiar with any important economic interests there, although they produce some oil and export it mainly to Europe (but it's small potatoes). So I'd assume it was geopolitics again, maybe Gaddafi was friend of Putin also.
Syria now is a complete mess with different local strongmen and terrorist groups competing for power, there's basically a constant state of anarchy and violence so I don't see how you can argue it was a good idea.