Because the GOP 'leadership' REFUSED to pay attention to him!
How many times are we going to get the football jerked away before we wise up?
Well it depends on what you mean by "wise up"? See, I think Perot ran KNOWING that the GOP wouldn't "listen to him." His PURPOSE was to split the party, to enable the CLintons to gain the most votes in the resulting plurality and win the election. Perot PICKED subjects he knew the GOP couldn't, or wouldn't, budge on - that was WHY he was "running," do do just that.
Now look at Trump - he's doing EXACTLY the same thing. He's picked a subject ALL of the GOP candidates are already vested in avoiding, because that's what their money-backers demand. So they CAN'T go where Trump is going, and Trump knows it.
That's why Cruz is being so smart here - he's EMBRACING Trump's position (which he already supported anyway, btw). Cruz is therefore not letting Trump split CRUZ. And, from that position, he's no doubt asking Trump how he wants to play it - to fail helping the Clintons because Cruz beat him to the position he's taking, or to join Cruz and make it stick, and maybe be VP or have a high position in the Cruz administration.
Cruz is wicked smart. Trump is too, but Trump looks in too many gilded mirrors and likes shiny toys too much - he's a bad boy who hobnobs with ALL sides to make deals. That's WHY he's a billionaire. And it's also why I think Cruz is offering him... dare I say it, LOL... a "deal."