Name of phenomenon where migrant workers receive decent wage but absolutely no chance of getting any government benefits
There's a lot going on in this question, so I'll focus on the labor-economics part of the question rather than the political-economy part of the question.

If it is the case that these migrant workers are being paid considerably better than their alternative labor options, but they are at the same time being deprived of rights they might value (access to social services, citizenship), then this is an example of a compensating differential.

The theory of compensating differentials says that, in order to get people to take a job that they'd rather not take (perhaps because taking it means they'd have to live as a second-class citizen), you have to pay them a little extra in order to convince them to take the job, "compensating" them for accepting the downsides of the job.

This explains, from a labor-econ perspective, why the workers might accept this arrangement. It doesn't explain the political system that deprives the workers of rights.