There are too many people that try to game the system. If the law exists, it is easy to find a loophole.
I know too many people that "hire" people (friends of friends or whatever) just to get the hiring reward for example. The reservation system in India mandates that you have to hire people no matter how poorly they have done in school. So, there are too many people that simple cry "caste system is against me", if things don't go their way and once hired, try to get the US H1-B jobs because at the end of the day the jobs are more lucrative 1 dollar != 1 rupee.
I also know waaaaaay too many people who have built massive wealth in India by simply sending money home and buying up properties. The idea being that once they own 5 or 6 homes, they just "retire" and live off the rental properties or whatever. So many of these same people have said "I don't give a shit what happens to workers here, as long as it doesn't affect me in the near future".
The only problem has always been those pesky border patrol officers who deny entry for cap, but now, if the cap is lifted, it will open the flood gates for a lot of these uneducated / uncaring / opportunistic folks who only want what is best for themselves.