I see this question come up often, and the basic answer seems a little obvious to me.
Mturk is basically interested in data entry. Data entry with a bit of savvy and expertise added.
I see people talk about 100,000 HITs over a year with 99% accuracy, and wonder why they can't get a Masters.
Getting a masters is all about data entry. Accurate data entry. Extremely proficient data entry.
You have to do 1000 HITs a day over and over again to get it.
You say you've done 100 HITs a day for a year with 99% accuracy? You won't get it.
Furthermore, a Master's is task oriented. You get it for doing certain tasks (categorization, photos, etc). You then get universal privileges. You probably also have to do a lot of other jobs to show your versatility.
The bottom line -- if you aren't a batch worker (a hard core batch worker who'll do 1000 or more of these a day, you probably won't get a Master's). You have to do this everyday for a long time before you get considered.
One other thing -- I'm not sure requestors who don't tend to reject (Crowdflower, e.g) matter much in this.