why question

why do so many people want to be famous?

 In my opinion I guess I would have to say that there are probably a number of factors involved. Primarily, one key motivation would be because they think they would be able to make more money. As well as this a subsequent incentive might be because they want to live in a big house and drive an expensive car.

reason:factor,motivation,incentive

why structure. begin with a linking phrase:
Well in my opinion I guess I would have to say that...
Well in my view, I suppose I would say that...
Well in my estimation, I guess that...
Well generally it's my belief that...

use a structure to say that"there are many reasons"
There are probably a number of factors involved.
There are obviously a number of motives surrounding this idea.
There are unquestionably a number of explanations for this.
There are undoubtedly a variety of justifications behind this.

introduce first reason:
The chief cause might be that...
The main basis is probably because...
The key explanation is possibly because...

introduce second reason:
As well as this, a subsequent factor could be because...
At the same time, a secondary motive could be that...
Additionally, a further rationale might be due to the fact that...