Many fighters use to take stay-busy fights between serious opponents. Tune-up fights.
Many top guys fought on regular network tv, no ppv. The fans got to see their favorite fighters showcasing their skills, and the fighter got to make a little extra cash with lower-ranked opponents between serious opponents.

There was no problem with it. It's just sometimes the mismatch resulted in an upset.
During Chavez' reign, he engaged in non-Title fights between Title defenses. Lower-ranked fighters who did not warrant a Title-shot got a payday out of it, and the chance of maybe pulling an upset.