The problem is that there is no agreed replacement.
Streeting is seen as continuity Starmer and is not popular within the party.
Rayner is popular with the party and would clearly be different, but her problems with HMRC are not yet resolved and some MPs think Rayner would do for the Labour party what Truss did for the Tories.
Burnham is seen as the king over the water, but is not eligible to stand as he is not an MP.
Ideally, Labour would prefer a coronation rather than a drawn out leadership campaign with the risk that the members will vote for someone unsuitable, but there is no sign yet of them agreeing on who should succeed Starmer, n or is there any sign that any of the leading candidates is prepared to stand aside in favour of someone else.
Unlike the Conservatives, the Labour party does not use a confidence vote to oust a leader. There is no mechanism for them to do so. The only mechanism available is the one West is trying to use - an MP getting 81 nominations to trigger a leadership contest.
If you mean he might lose a confidence vote in the Commons, that is highly unlikely. That would require a lot of Labour MPs to either abstain or vote against him, knowing that he would probably call a general election if he lost.