If they don't want to hear the case, they shouldn't be allowed a vote

As many as 15 seats of Republican senators were empty during the first few hours of the trial Thursday, compared to just a handful of Democrats who were outside of the chamber, according to pool reports.

[...]

Many within the chamber were preoccupied with other activities: Sens. Tom Cotton (R-Ark.) and Chuck Grassley (R-Iowa) were reading papers, while, according to CNN’s Jeremy Herb, Sen. Rick Scott (R-Fla.) “had a blank map of Asia on his desk and was writing on it like he was filling in the names of the countries.”

[...]

Even Trump’s lawyers were checked out, with David Schoen and Bruce Castor reportedly not taking notes and Schoen even leaving the chamber to speak to reporters and participate in several TV news interviews.

  Forbes

Well, that's not surprising, as they know no matter what they do or don't do, the case has already been decided.

“It’s the same as yesterday and the same as the day before… it’s just redundant. The same thing, over and over again,” Sen. Jim Inhofe (R-Okla.) told reporters of impeachment managers’ arguments on Thursday. “To me, the more you hear it, the less credibility there is in it.”

If you're a Republican, you don't have to make sense.

...but hey, do what you want...you will anyway.