Basically it was a long demoralizing campaign on Syria and the SAA waged by NATO, where the currency was crushed and the state budget dried up through sanctions and theft of the country's main resources (oil, wheat, potash). apparently the soldiers were very poorly supplied, paid and fed, while the rebels had top of the line equipment including night vision goggles, armor etc. The SAA looked like a ragtag rebel force while the rebels looked like regular soldiers.
As well the rebels had top of the line US/NATO EW tools that disrupted the SAA chain of command, which was carefully mapped out and scoped by US/NATO, Turkish and Israeli intell.
A lot of the blame here is on Russia and China, they should have supported the Syrian economy and supplied their army. Assad lost the support of the middle class in the cities by not being able for several years now to provide basic services and necessities (power, fuel, public service salaries, benefits etc). The Chinese in particular should have been involved because their Uyghur jihadi trash are a large contingent of the rebel force. As well the Russians have plenty of oil and wheat, they gave away lots of it to African nations, they should have picked up the slack in Syria.
If NATO hasn't been pumping tens of billions into Ukraine, their currency and economy would have long collapsed, payments to civil servants and soldiers stopped, services very limited. Their army would have cratered long ago. This is what happened in Syria.