Osteen comes from a certain segment of the Christian movement, so of course people whose background is in a different denomination, etc. are likely to call him a heretic or something like that.
But he's best known for his TV broadcasts, not for what goes on at Lakewood Church on a daily basis. That being the case, he meets a certain need, and he does it well. The same can be said of Joyce Meyer, who is similarly criticized on theological grounds.
But for people who are NOT strongly rooted in the beliefs and practices of one denomination or another, who are searching, not regular church members anywhere, and are uncertain about God in their lives...these TV preachers probably do serve a need.
That's not to say that ALL such TV evangelists fit that mold, but these two probably do, and a few others who could be named. That's why it is possible to disagree with some of their theology but, at the same time, acknowledge the good that they do in reaching people, and that this is something not every local pastor can do.