If a Prophet comes and says "I ask you no reward in this in form of money or anything, but to follow me", people can interpret it that the Prophet is power hungry, and it can give a wrong impression.
Most people seem to always value more to have power and authority then wealth. Or at least a lot of people do.
The same is true of saying "I ask you no personal wage for it but if you want to be grateful to God, the God's wage for the message is to follow me". The way the human mind works, it will think, wait a minute, this person wants to be followed and is saying he asks no reward but rather it's God asking us a reward and that is for him to be followed.
The Prophets also cannot say "but to follow the Prophets" as they are one of the Prophets, and hence, the same non-eloquent matter would be problematic.
However regarding the family of Mohammad who are not Prophets, the Quran can be saying: say: you seek no personal reward rather your personal reward is with God, but rather say the wage you ask for the message (on behalf of God) is to take a path to God...now before you say AHA he is power hungry and of course what he means by that is obeying him and following him as most of Quran emphasizes on, while it's true following me would be following God, what I'm actually asking is to love my family if you want to show appreciation to this message, that recognizing them as guides and attaching yourself to them is the means to God, and not only that but the whole Quran has shown wisdom in chosen guidance through chosen succession of guides one after another who are related both by blood and by a bond that cannot be appreciated in normal language.
That it is in fact, not only something I am asking you, but it's a reminder to the whole world, that anyone from the whole world will take a path to their Lord if they love my family.
Now before you accuse me of favoring my bloodline, look, at Quran, look at how God has chosen people in the past, look at the wisdom in it, indeed it is but a reminder to the worlds.
And this has an eloquence, because it shows, Mohammad trusted a certain people to continue his way, to manifest his guidance, to be the way to God and take his position. That he is not asking to really follow him alone at the end, so that people say he is power hungry, but rather he believes others ought to be followed with him in the same capacity.
This if you really think about it, and with how Quran talks about the story of Yusuf and keeping in the background of Yahya inheriting Zakariya, and how much Quran emphasized on this theme linked to chosen families, that this is no doubt a huge indication of the truthfulness of the message.
Allah saying, if Mohammad truly was doing all this as a reward so he can be followed, why would he would entrust the message to his family, and yet emphasize in Quran that of the offspring of Abraham were guided people and that many of them were unjust people.
How would he know the few of his offspring that can take on this role of leadership, how can he expect them to put on act and pretend they are divinely appointed while at the same time, having to maintain the exact same message?
More over, if anyone understood something from Quran that they didn't or had more knowledge then them, this would invalidate them being his chosen family, and they aren't Guides chosen above the world.
One of the wisdom is that it manifests clearly Mohammad was not power hungry, and in mutuwattir saying the Nabi said:
"I am leaving you two weighty things, Quran and my family...."