There's definitely some truth to this, FreeRADIUS is just not that valuable of a target since not many people have RADIUS exposed to the world, however if you look at other highly valuable targets like OpenSSH, which is probably in the top 10 if not the most valuable target in the world, you see far fewer significant exploits. It's definitely possible to have better quality than OpenSSL and a lot of OpenSSL's issues are due to legacy code and what amount to experiments being run in production software.