[seren]

It is a double edge sword : some volunteers are still in contact with their family at home via Skype or other mean. If you cut them off totally, you have no hope of winning them back.

Another point is intel, there might not been a lot of sources in occupied territories, but at least some of them are sending information, likely via internet.

According to wikipedia [0], SOHR has 200 informants in Syria. It is not said where exactly there are, but for example, there are reporting this morning that 33 jihadists were killed last night in Rakka. Obviously this is coming from someone in Rakka.

And lastly, there is also a large population of civilians in there, this is why as far as now, no one is bombarding critical infrastructure like water, electricity.

[0] https://en.wikipedia.org/wiki/Syrian_Observatory_for_Human_R...

It might be technically possible but not necessarily a net gain in the end.