[mwnz]

Yes, but that greencard processes like the EB2 take a very long time. It is difficult for an employer to sign up an employee, with the hope that they begin work 12 months later. This processing period can easily balloon out due to random audits.

Granted, the H1B process is slow too.

[NhanH]

The H1B process is slow, but pretty much deterministic within a period of few months (every year). On the other hands, the EB1/2/3 and various O visa is very indeterministic (you won't know what happen, for how long), especially when those varies depends on the country of origin.