Just guessing

Let them make their sentiments known on the the actual Ariticles of Impeachment and stop the phony posturing on a vote that the Speaker doesn't have to hold as it's not required by the Constitution. She runs the House, not them.

1 - A formal vote on impeachment can give subpoena power to the minority (Republicans) (See: https://www.latimes.com/politics/story/2019-10-07/subpoena-power-republicans-want-house-vote-impeachment-inquiry-pelosi-doesnt ).

2 - It forces Congress members to take sides which can be a political advantage.

That's exactly the kind of thing I was looking for.

I've seen several posts and conjectures that a formal House vote "might" or "could" give the minority subpoena power. Yes, during the Nixon and the Clinton impeachment proceedings, the minority had the power to propose subpoenas, subject to a full vote of the committee. Since then, however, Republicans changed the rules for committee proceedings, arrogating to the majority virtually all power in the committee. If impeachment proceeds under the Republican rules, the minority won't have any more power in the committee than it does now, which is el zilcho. #legaltermofart

We don't know what would be in any "impeachment authorization" bill or motion, but I'm confident that Pelosi wouldn't bring something to a floor vote that would give away the power the majority now enjoys courtesy of the changes the Republicans instituted in (I want to say) 2015.