They were able to remove McCarthy for two reasons-

1. No Dems would support him at all because he went on the Sunday talk shows and disparaged Dems in the House- basically he lied to the Democrats and then tried to blame them for stuff not getting done- he lost complete trust.

2. Those wanting to oust Johnson do not have the votes this time even in their own caucus.

The GOP rank and file are starting to catch on that the performative chaos is making them look bad and won't support it anymore. Some Dems maybe would vote to support Johnson given his compromises to aid to Ukraine, especially. Johnson came in wanting to stop Ukraine aid- very trumpish. But reportedly, as a member of the "gang of eight" (set of eight leaders within the United States Congress who are briefed on classified intelligence matters by the executive branch.) what he heard in the briefings "scared him." Very likely much had to do with Russian actions if Ukraine fell- Baltics and Moldova next with Putin daring NATO to do anything