The problem is not THEM. I actually don't think there is a problem here, except the one you have created. You are unhappy and disgruntled that you were deactivated. As you noted, there are plenty of other MSCs to work for. Why waste time feeling sad and blaming the MSC because you were unable to meet expectations at that particular MSC? Take responsibility. Own up to the failure, learn from it, and move on.
I respect companies that proactively review the performance of their independent contractors and continue to use only those who excel. With a large group of shoppers registered, a company can afford to cut the lower-performing ICs. The MSC is not going to lose their better shoppers because word gets around that they deactivate those with low scores, two rejected reports, and a failure rate of 25%.
Over 25 years of living in the same home, a major fixer-upper, I have used many independent contractors. If I am dissatisfied with one of them, I don't use him again. I use a different contractor. Perhaps that is an "unforgiving" attitude, but I want the very best for my dollars spent. When I have contractors available who do excellent work, why would I pay for less? I don't "owe" a contractor who did a bad job another chance. I work with the very best, some for many years. For example, I have used the same plumbing company for 25 years - they are outstanding - and for the last 17 years I have used the same plumbing employee at that company - I always ask for him.
It's time to just move on to other jobs and other companies.