The ruling power in any country can lose popular support but maintain its rule by being brutal. But there’s a tradeoff between brutality and popular support. The more brutal, the more power, but the less support. There’s a fine line to tread and once you go over the brutality-too-far line the support drops to zero and no additional brutality can suffice. Assad had passed over the line and it was the Russian supplying the brutality and the Russians couldn’t keep up the brutality and their other obligations. Once the Russians pulled the brutality plug there wasn’t a sufficient supply of loyal Assad people to keep up the required brutality.
On the other hand, had Assad not started the brutality trajectory during the Arab Spring, he’d have been out of power long, long ago. Was it worth it? His personal wealth was estimated in the billions. But reportedly Putin has seized Assad’s wealth. Damn! Bad luck, eh?
Wagner Mercenaries and Hezbollah provided the brutality in Syria.
Putin had to use his Mercenaries in Ukraine. Iran decided to attack Israel with Hezbollah. All of a sudden, Assad is exposed.
Also, I wouldn't be surprised if most of the pilots manning the helicopters and planes were Russian. But now they're all in Ukraine. So Assad can no longer have air support to take out the enemy before they attack.