Western powers don't support the Sunni forces. They supported the Kurds off and on, who are one of the most democratic and multilateral governments in the middle east, but it was the Sunni forces who overthrew Assad.
The US definitely didn't like Assad using chlorine gas on civilians, and called airstrikes on his military occasionally, but Obama, Trump and Biden never strove for a regime change there.
This regime change was caused by Syrian economic issues, Turkish aid, reduced infighting between the Kurds and the Sunnis, and the collapse of Russia's illegal Wagner PMC.
Yes. It was one of the countries that weren't sucking israel's dick so it had to go. Just look at the pattern of all the other Middle Eastern countries that have been regime changed.