I can tell you exactly why they went to paid recruiters.
While some people understood how important it was, a number of the corps considered Phone Push to be a huge waste of their time. Consequently they wouldn't do a good job of following through on the lists, or they would call a small number of people and spend the rest of the time goofing off. Also the smaller the outfit was, the more Phone Push duty individual cadets had, which when a few cadets in the unit were unmotivated could make a big difference in recruitment success. That wasn't the main reason why they switched over, though.
They found out that some cadets were not calling any of the women on the sheets. Others were calling the women and telling them not to join the corps. In some cases this was unofficial outfit policy. An extremely small number of cadets were even asking what race or religion the candidates were and advising minorities not to join. In some cases a potential candidate would get a phone call advising them not to join one week and then a followup call from a different cadet a couple of weeks later with a completely different attitude.
Also very little Phone Push training was done, and so some callers would make wildly inaccurate statements about corps policy, administrative policy, academics, etc. Some had poor phone etiquette and didn't make a good impression on candidates or parents. There was very little that could be done to discipline those who were not taking recruiting seriously or were abusing the system.
In the end they decided to go to paid recruiters because they were objective, received training, they could be a consistent contact for potential cadets, they weren't losing study time by calling, and if they screwed up or didn't do their jobs they could be fired. Shame it had to be that way, but it's a pretty prime example of a small number of cadets screwing it up for everyone.