It’s folks like Kasich and Carson who are enabling Trump’s majority based on a split vote. These two should have dropped off after Iowa. On a one-on-one, Cruz beats Trump.
Kasich and Carson’s votes could have all gone to Cruz and he’d still be struggling to compete with Trump.
If they’d dropped out after New Hampshire, their voters would have wound up splintering themselves amongst the remaining candidates.
Heck, most of them might have even gone to Trump, for that matter.