Up until this week, Trump has had more support from the senate than Cruz does.
He’s used that as means to hit at Cruz while trying to maintain that he isn’t a part of the establishment and Cruz is. I know, pretzel logic but there it is.
Now that Cruz is going to have a list of supporters it’s all of a sudden “See, he is the establishment choice!”
I think the reality is:
Some senators waited to see how things were going before endorsing a candidate.
Some Senators are freaking out about trump and are willing to endorse Cruz because they care more about the country and party than they care about the idea that Cruz will call them out for helping democrats.
Some Senators probably think Cruz has a real chance and want to go on the record as supporting someone other than trump.
I think more accurately, the GOPe just ran out of all other alternatives to Trump, and Cruz is the only possibility left, so he’s the one they have to go with. They certainly don’t like Cruz, but Trump has always been the one the GOPe fears most because of his opposition to their globalist immigration and trade policies.