Writes the Bionic Mosquito:

This Cruz / Kasich thing is fishy.  I think it is one more sign many in power want Trump to win. [Because they to avoid  a neocon WWIII.]

Why did Cruz / Kasich announce this publicly?  They could have just done it, each saying that they are just focussing on their strong states.  No one would have blinked.

Or just say nothing.

By making it so public, they only energize more support for Trump.  That is the only benefit of being so public about it.