Why is it common for pastors to advocate leadership (including their
own) when it is easy to conclude that it is anti-biblical according to
what Jesus had said?
I am not so sure that pastors advocate "leadership" so much as they advocate following. The hallmark of a good leader is the ability to follow commands, not give them. All pastors, if they are walking in their calling as God intended, are themselves "following" the directives God has given. Therefore, those pastors would be imploring the members of the church to likewise follow the one whom the pastor follows. Still, there is Scriptural precedent for a pastor to plead for leadership—
Feed the flock of God which is among you, taking the oversight
thereof, not by constraint, but willingly; not for filthy lucre, but
of a ready mind; —1 Peter 5:2 (AV)
There are definitely those in the church who are appointed to a position of leadership. This position of leadership is not to be used to lord one's self over others, nor as an avenue for imposing one's own will, plan, or purpose upon others. This position of leadership is primarily for structure and unity within the local church body. Peters words are clear; those in leadership are to "take" the oversight. They need to step up and be accountable, reliable men and women who will feed the flock (church). They should not be in ministry (especially not in a leadership capacity) for fame, or fortune. Again we see from the book of Acts—
Take heed therefore unto yourselves, and to all the flock, over the
which the Holy Ghost hath made you overseers, to feed the church of
God, which he hath purchased with his own blood. —Acts 20:28 (AV)
One does not simply "volunteer" to be a pastor or church leader. One is "made" so by the Holy Ghost. It is a sobering thing to be called out to feed the flock of God. That is why james tells us—
My brethren, be not many masters, knowing that we shall receive the
greater condemnation. —James 3:1 (AV)
Those who are called to teach and feed the flock should definitely take heed to themselves knowing that they are responsible for speaking the truth to the flock of God. Church leadership os no place for theory or conjecture; it is serious business with eternal repercussions.
Your quote from Matthew 23 is pointed directly at the scribes and Pharisees who enjoyed the accolades of the crowd, the attention that their position brought to them. This is the wrong reason for being in ministry. Yeshua's directive is, "...do not seek to be called a master/teacher/leader/whatever." If you are a leader; then lead. If you are a teacher; then teach. But in no case should you seek glory from men.
A final thought here should help put things in proper perspective. One of the gifts that yeshua gave to the church was the gift of people as seen in the book of Ephesians—
And he gave some, apostles; and some, prophets; and some, evangelists;
and some, pastors and teachers; 12 For the perfecting of the saints,
for the work of the ministry, for the edifying of the body of Christ:
13 Till we all come in the unity of the faith, and of the knowledge of
the Son of God, unto a perfect man, unto the measure of the stature of
the fulness of Christ: 14 That we henceforth be no more children,
tossed to and fro, and carried about with every wind of doctrine, by
the sleight of men, and cunning craftiness, whereby they lie in wait
to deceive; —Ephesians 4:11-13 (AV)
The last gift on the list in verse 11 is "some pastors and teachers." You will notice that it does not state some pastors and some teachers, which would separate pastors from teachers. A pastor is a teacher, a leader in the church, a man or woman whose life is to so emulate Messiah so as to be an example worthy of following. this is one reason why Paul says to be followers of him (1 Corinthians 4:16; 11:1).
All of those gifts of people are, according to Ephesians 4:12, for the perfecting of the saints for the work of the ministry, for the edifying (building up) of the body of Christ. That, necessarily speaks to a position of leadership; which leadership is best done by example, not by mere speech. People need to hear the truth, but beyond that they need to see the truth put into action whenever possible.
Ephesians 4:13 gives us a clue of how long we may expect to have these gifts of people in the church; "Till we all come in the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fullness of Christ;" We are still very much in need of these leaders in the church. We do not need men and women TELL us the way, we need them to SHOW us the way. Israel needed Moses to SHOW them the way.