This seems pretty simple to me.
The president appoints Supreme Court justices.
The Senate acts as a check on that, by vetting and approving (or disapproving) the choice.
This Senate is neither vetting nor disapproving of choices, they're simply saying "No, we won't let the President appoint someone."
It would be one thing if the Senate objected to various potential justices, but it's not even that. It's literally, "We don't like this, so let's shut down this entire process."
It's not that surprising- that's basically been the Republican strategy for all of Obama's tenure. I live in DC, I remember when the GOP literally let the federal government shut down for a week out of spite.
Saying "There's nothing in the Constitution that says the Senate has to vote on a nominee" is silly. It's like sitting in the backseat of a car with your brother and going "Ha, ha, I'm not touching youuu" while waving your hand in front of his face.
My original point was that it's embarrassing. It's not an example of good governance, or honorable behavior.