Because that is how rare Mayeux talent was in the Steppe. Aeryon could even say he is truly lucky to have such a person.
While it is undeniable that Aeryon and Belarion is the one that expanded the tribe, without Mayeux, it would not be as orderly or as fast as it is without having some problem on the rear.
The same for Burchu. With his spear skills, there is no place in the Great Steppe that he could not thrive
Instead, he choose to ride his horse to serve Aeryon.
That is because he believe that only Aeryon could let him have the stage to show his abilities
Capable people could choose and the weak could only accept.
This invisible prestige could sometimes help and who knows how many capable warriors right now is tempted to selling their skills to Aeryon?
The other tribes chief, some of them is wise and could see that Aeryon reputation rising is not exactly good for them.
Some only saw the short-term disadvantage of Aeryon action and deed but not the long-term advantage.