I think it’s important when you consider that a whopping 46% of Republicans don’t have either Trump or Cruz as their candidate. When others start dropping out, the favorability of second choice candidates will be most important, as well as the endorsements by these former candidates.
The whopping 46% is still spread among four or five candidates, then others who have one or two percent each. Some of that 46% will go to Trump and Cruz, and these popularity polls change faster than polls that measure who people intend to vote for.