Probably because they feel guilty at being able to live the good life and never having to have worked for it
I think you are very close to the real answer here, thanks for helping me to clarify this puzzling situation.
I would add that the left does not recognize their lack of work as part of their problem, but instead have focused on Christianity and the white man as tangible manifestations of the bad guys for 'stealing' this beautiful land from the noble savages they found here (plus a host of other factors they see as evil, like slavery, etc.).
The Muslims are just the lefts tool for punishing the bad guys as the left rises to power to fill the vacuum. They don't seem to realize the Mooslims see them the same as all other Kafirs and won't just go away when the fighting is mostly done.