Well it’s not that simple. For one thing, Kevin McCarthy was recently drawn into a district that was traditionally blue. While it’s not totally clear how things are going to shake out, him not running again is likely going to change that into a tossup race. A MAGA candidate isn’t really going to do well there anyway.Honestly, it isn't something to be celebrated. Most quasi-MAGA or opportunistic collaborators (as well as any traditional, anti-MAGA) leaving congress will be replaced by real MAGA's in the districts not won by dems.
Add to that, McCarthy was one of the house GOP’s best fundraisers and helped deliver the majority and put those MAGA candidates into their seats. Anything that can chip away at the GOP’s campaign arm is going to matter in what’s going to be a close house race. And it does matter, just ask the Senate Republicans.
Edit: also not sure what special election rules are, but between this and George Santos the GOP is serious compromising its thin majority. This is going to create real problems for any impeachment or other legislative goals for the election year.