Ok, so you are referring to McConnell, who said that he thought the Senate lacked jurisdiction, and that it would be unconstitutional to convict. Senator Blunt also considered it "unconstitutional". Yes, I suppose these would be "technicalities" if members thought the proceedings were not in accord with the Constiution, but that would be a pretty substantial 'technicality". However, other senators, such as Cruz and Hawley, said that they did not find convincing the argument that Trump somehow did something wrong.
So in other words, Republicans acquitted because they thought the impeachment was unconstitutional and/or they did not think that Trump commit deeds worthy of being convicted.