More info about contested convention rules in the NY Times
You should read this short, informative, and well-illustrated article in the NY Times which provides some more information about contested primaries and how delegates are selected.
Because there hasn’t been a convention since 1976, forty years ago, when a candidate didn’t go in with a majority of the delegates, and even that convention was only barely contested–when there are only two candidates to vote for (Ford and Reagan), one of them has to win on the first ballot unless there’s an very unlikely tie vote–people don’t know anything about the process and there’s a lot of misinformation and bad assumptions floating around.
I think it’s interesting that Ohio is a unique state in that (1) it’s winner-take-all; and (2) the winning candidate gets to handpick 63 of the 66 delegates. That means, if Kasich wins, there are going to be at least 63 loyal Kasich supporters at the convention, which is a huge advantage for Kasich.