I haven’t been following it but based on memory it seems to me is follow the oil and those who want it.
In 2009, Qatar proposed to run a natural gas pipeline through Syria and Turkey to Europe. Instead, Assad forged a pact with Iraq and Iran to run a pipeline eastward, allowing those Shia-dominated countries access to the European natural gas market while denying access to Sunni Saudi Arabia and Qatar. The latter states, it appears, are now attempting to remove Assad so they can control Syria and run their own pipeline through Turkey.
The standard Shia-Sunni conflict is little different from many other socio-ethnic-economic-political-religious (SEEPR) conflicts that originate in competition for resources, but in Syria it has a lucrative twist. The pattern of SEEPR control in Syria is similar to that in many other Middle Eastern and sub-Saharan Africa countries (and is arguably common in every country, but more so in traditional societies): Who controls the government controls the state’s resources, and by extension, the wealth derived from them. In Syria, the Sunnis have tried to unseat the Alawites ever since France installed them during the French mandate that ended in 1943. But now the stakes are higher, thanks to natural gas.