JWs are instructed to cultivate an attitude of unselfishness and empathy. Those who focus exclusively on their ego's are normally very proud and selfish and have no considerations for others. That kind of attitude is completely against our beliefs. We are taught to love each other and a big ego would lead us to the opposite of love.
Here's a few scriptures that back our beliefs:
1 Corinthians 10:33; 13:4-8; "just as I am trying to please all people in all things, not seeking my own advantage, but that of the many, so that they may be saved." , "Love is patient and kind. Love is not jealous. It does not brag, does not get puffed up,
does not behave indecently, does not look for its own interests, does not become provoked. It does not keep account of the injury.
It does not rejoice over unrighteousness, but rejoices with the truth.
It bears all things, believes all things, hopes all things, endures all things. Love never fails. But if there are gifts of prophecy, they will be done away with; if there are tongues, they will cease; if there is knowledge, it will be done away with."
Galatians 5:26; "Let us not become egotistical, stirring up competition with one another, envying one another."
Philippians 2:3, 4. "Do nothing out of contentiousness or out of egotism, but with humility consider others superior to you,
as you look out not only for your own interests, but also for the interests of others"