I take issue with your conclusion that "if the workers are correctly concluding this their best option, then cheers to Mechanical Turk for improving their lives to some extent". A less generous interpretation is that Amazon has identified a cohort of people with limited employment options and found a way to effectively pay them less than minimum wage.

Is any job better than none to an unemployed person? Maybe — but we need money to live, and labor laws exist precisely to prevent employers from exploiting that.