Probably because his fights with Mosley and Ortiz were in the top 3 money making ppv's for non heavyweights, you can bet the Cotto fight brought in more money than that too so now he's well in the driving position for a bigger split, at the time of Pacquiao beating Cotto Mayweather had only had one fight that drew that much ppv and that was Oscar. As for him avoiding all of the top boxers, he had an 8 page contract and Pacquiao refused to sign it so it wasn't Mayweather avoiding anything, all Manny had to do was sign it and we would have had the fight by now.
Nitpicking?, which obviously means you have no answer to my post. It is nitpicking to you but it surely isn't nitpicking to the fighter subjected to those tests during training camp. Of course Mayweather has more to lose, Pacquiao has A LOT to lose as well, not more than Mayweather's 0 and reputation but he definitely has a lot to lose. For one thing, Pacquiao might be accused for using steroids in previous fights by a lot of fans if Mayweather makes him look bad and beats him.
Floyd stipulated a test that was unconventional which PAC didn't agree so, Floyd should get the blamed for it. If it were the other way PAC would have been to blame but, it wasn't. Your lines above doesn't explain why Floyd didn't fight all the top guys when he should have.