That's the problem. GitHub brass thinks their most important constituent is the people paying thousands of dollars to buy GitHub Enterprise. The only reason they have the enterprise customers is because they got popular with open source first. However, at this point their enterprise popularity may be big enough that success there is self-sustaining -- enterprises make decisions based more on what other enterprises do rather than on what open source and small companies do.

That being said, I bet that enterprises are screaming about Issues too. Enterprise loves their custom fields.