It is lot easier to decide to move to Canada if someone was in India as someone working in India sees improvement in pay, standard of life etc etc when they move. It ends up as worth a struggle for them. But it is not the case with people who are already comfortably living in US. They need to compromise on many fronts like salary, savings, career etc at the cost of immigration stability. Most also don't like the initial struggle associated with any immigration move, and get a feeling that why should I leave a better place and suffer here. I believe that holds back a lot people. Also now that they are allowing spouses to work with H4 EAD, it holds back even more people who then had justification of spouse work/career as a reason to move.
I have seen a lots of people having this "pursuing US GC vs Canadian PR" old posts (say 2011 - 2012 time frames) in trackitt. When I check their profile to see what they finally decided, I noticed that 99% of them continued to stay in US, closely following the immigration developments and hoping for a miracle since then. Some gave up on Canadian PR, some desperately try to look for options to extend the PR without meeting residency obligations. Forget GC, none of them are even close to EAD yet. Some times I feel, if they had made a hard decision to move at the time they had posted those threads without thinking too much, they would gotten Canadian citizenship or would have at least been close to citizenship by now.
I don't know.. I am just working for my PR, with a PD in 2016, honestly I don't know what will I do if I ever get one. From what I am observing, it is not going to be a easy decision to make at all. US is like a magnet for Indians.