They did use the 2 piece uniforms years ago. Only a few schools used them part time.. I remember Lehigh and Hofstra using them.. didn't really catch on. I think most wrestlers like the singlet. It's the nonwrestlers who now have 1 less excuse to give when explaining why they don't want to wrestle, that don't like them.
I don't know why so many people have forgotten this. Chattanooga, The Citadel, Hofstra and Lehigh are the only teams I remember using them, and I think Lehigh only used them part time. Chattanooga, the Citadel and Lehigh used them the entire season, including conference and the NCAA's. There is video found easily enough of Charles Griffin wearing one Vs Teyon Ware. This video is over 10 years old, and people act like the idea of shirts and shorts is something new.
I've never worn them, but compared to a singlet, they look extremely uncomfortable. If you watch, Griffin is consistently tugging at the shirt and the shorts.
Looks I'm sure is a concern, but I would think comfort would be one too.
Hence why so many schools now have singlets that come just above the knee vs the old school ones that road the crotch something fierce. Jam length, I think is what they call it.