I had a suspicions of it coming for months, and I am certain I am not the only one, just thinking about how much Assad's allies were all getting depleted by attrition.
Strategically, he was backed by Lebanese Hezbollah, by Russia in air power, and by Shiite militias of mostly Iraqis, but militarily backed by Iran and the IRGC. That was in response to the original civil war actions where Turkey was backing the HTS/Nusra Front/Al Qaida proxy army, Saudi Arabia and the gulf oil states were backing ISIS (with US help, depending what they were targeting), and the US & Israelis backing the Kurds (but only the more right wing faction which had helped them in Iraq, not the more leftist PKK which has a blood feud with Turkey). Once Assad slowly beat back the great initial danger from the rebels, the situation was fairly locked in for several years, but this last year's events basically weakened Assad's allies, drawing their strength away to other fights, from which it could not return. Russia has to devote all its meaningful resources to the Ukraine war. Iran was doing what it could to help the "Triple H" allies (Hezbollah, the Houthis, and Hamas) regarding Gaza, but facing a US/Israeli war machine in all those cases, which has essentially unlimited resources, so two out of those three were very quickly fucked. Honestly Iran should have pulled Hezbollah back from it, and advised them not to do sympathy attacks over Gaza which would give Netanyahu to wage yet another war he always wanted; Hezbollah's actions basically did nothing for Gaza and lost Syria. (Might lose position in labanon too, just wait and see). Assad's government lost basically everyone backing him up, and I have no doubt that the "sudden" rebel advances by HTS were actually well-orchestrated by Erdgan's government in Turkey, likely with Joe Biden's help (he is trying to do as much as possible to change international war situations and make them irreversible, before Trump takes power). Once Assad has lost Aleppo, there was nothing material-wise or morale wise to stop the HTS offensive from just rolling on and on. It really reminds me of what happened in Afghanistan with the Taliban taking over again, and much like there, I think you will see this new jihadi government try to put on some "nice guy" image at first, to get international recognition and a lifting of sanctions. Once they get it, bloody purges of Syria's various "infidels" will begin.
