His Army couldn't hold the majority of those places you talk about, that's why he called in Iran, Hezbollah and Russia to save his ass.
A nation called in its allies to support it in its fight against a foreign backed insurgency, conflict by proxy. If over half of Syria supported the opposition, why have so many refugees admitted to fleeing IS and AL-Qaeda, and why does the Syrian opposition need so much support from tens of thousands of foreign fighters. You also forget to realise that when we talk about the Syrian Army, they have lost tens of thousands of SYRIAN born and bread soldiers to forces backed by foreign states filled with foreign fighters.
I don't know where you live, but just imagine a similar scenario unfolding on your doorstep, imagine Russia started backing communist rebels in your country, who would you side with? Your fellow communist sympathising countrymen, or your government that was elected and is run by your fellow countrymen?