It's unfortunately a vicious cycle, the best avoid hard fights to protect their 0 losses, and then maintain unrealistically perfect records, which then means anyone who does lose that 0 loses a lot of credibility as a top fighter, and thus money, which of course circles back to them doing all they can to protect their records (and income).
If the best boxers are really mandated to fight good opponents, a lot of them lose their perfect records, and it's Ok (like most other sports), they're still recognised as great as their records will still be impressive.
In fact, I feel it will ramp up interest with fans (and income) as fights will generally be more exciting with more jeopardy.