The follow on. Lots and LOTS of unrelated changes can be a symptom of an immature codebase/product, simply a new endeavor.

If it's a greenfield project, in order to move fast you don't want to gold plate or over predictive future. This often means you run into misc design blockers constantly. Which often necessitate refactors & improvements along the way. Depending on the team this can be broken out into the refactor, then the feature, and reviewed back-to-back. This does have it's downsides though, as the scope of the design may become obfuscated and may lead to ineffective code review.

Ofc mature codebases don't often suffer from the same issues, and most of the foundational problems are solved. And patterns have been well established.

/ramble