That always happens. The voters don't all go on the web, do a complete investigation of every other candidate's stands on the important issues and then switch to the one who most resembles their fallen hero.
That's what FR posters do. That's what political junkies of all kinds do. But most voters, even GOP primary voters, don't have 5% the interest in politics of your typical FR poster.
A Jeb voter who switched to Trump never really understood Jeb or they don't understand Trump or, even more likely, they don't have a clue about either.
The proverbial low information voters are part of every candidate's pool of supporters. In the case of a mainstream media touted "frontrunner" like Jeb I suspect more than average. When Jeb collapses many of them look at CNN headlines and say "Trump is winning, guess I'll go with him. Looks presidential."
That's why from here on Trump will easily exceed his ceiling all the way to the nomination.