Fighting is as much about morale as it is about numbers and equipment. Morale was low and sunk lower after the anti-Assad militants had big successes, things snow balled from there.
All the allies who helped Syria last time are stretched thin by Israel (Iran, Hezbollah), have bigger concerns (Russia), or otherwise 'saw the writing on the wall' given the situation with Syria's other allies (Iraqi militias).
For Israel's part, they've bombed key targets in Syria during the last year.
We live in a dark timeline. The resistance Axis wasn't as strong as we thought and the Israel has proven more ruthless (and uncle Sam has an endless willingness to arm them). It's not over though. It took decades for the Vietnamese to win against the imperialists.
Every one tries to make friends with the new government of Syria (assuming there is one). There have already been statements from Assad's allies )Iraqi militia leaders, Iran and Russia) expressing interest in diplomacy.
I'm not optimistic, but the future isn't certain either.