Unfortunately, voting systems aren’t simple, and bad voting systems (in particular, systems where vote-splitting is a problem, such as choose-only-one voting) obtain bad results. We considered using straight approval voting, but MCA-M (which is categorically an approval system) provides voters the ability to express greater nuance.
The objective was to have a polling method that would (a) allow voters to accurately reflect their preferences, (b) obtain a majoritarian result, and (c) fit within the constraints imposed by what is supported on Helios. MCA-M was the simplest system that satisfied all of those criteria, and having seen the results I think it served admirably for that purpose.