>>713524710
The Saiyans were deliberately kept as cannon fodder fighting trash mobs the Freeza Force proper couldn't be bothered to deal with, which kept the Saiyans complacent and docile. If they ever truly realized that a Saiyan's power was theoretically infinite and they grow stronger when faced with more powerful opponents they absolutely could have proven a threat to Freeza and his empire, so he destroyed them before that could happen.