First off, he's a Senator. We all know that pretty much everyone in the Senate, with the possible exception of Mike Lee, HATES Ted Cruz.
Second, the fact that all these endorsements are coming after SC and NV tells me that a lot of cowardly political figures were waiting to hop on a bandwagon to endorse who they thought would be the eventual winner. Never mind, of course, that even in the Democratic primary, South Carolina showed some downright weird results (Hillary 3 to 1? You kiddin' me?).
Yet South Carolina, the same state where primaries brought us Alvin Greene and the reviled Lindsey Graham avoiding a runoff by winning more votes than all seven of his competitors combined, was treated by the press and many here as Ted Cruz's Waterloo. Now Trump gets the endorsements of a frontrunner.
It just goes to show the incestuous nature of politics (no pun intended) and the eagerness of politicians to hop on a supposed outsider's bandwagon if the opportunity looks right.