Then you must not be from the region or have sufficient familiarity with it. Let me just give you some context (and I'll preface with saying that I support the YPG; or at least I much rather them win over bashar or the other rebels)

• the vast majority of the population is under Assad's government's control
• The people of the region, no matter under whose control, are suffering immensely. Oil and wheat are the most important resources in the region.
• there's no electricity in Syria right now, the production of which is tied to oil supply. The vast majority of Syrians get about 1 hour of electric power per day. This means that Syrians can't use fridges, they can't stay warm in the winter, or have partly reliable transportation. Not even hospitals can power their ancient equipment reliably. The number of people starving to death remains undocumented and concealed by the government

So while we can talk about how nice it is that YPG can make profits from oil, the vast majority of the region's population are starving and dying from cold due to the lack of it. And I hope you understand how hard it is for me to keep my cool writing this, because someone on the Internet thinks the group claiming their preferred ideology should continue hoarding oil supply to please the US, and starve people. I keep my cool because I assume you have good intentions and did not know the above facts (since unfortunately media no longer thinks we're important). I hope you reconsider your position (not that it'll save our people. They will starve for the foreseeable future unfortunately. But at least it gives me peace).