Looking at the change history of the autobuilder, it looks like this change was on purpose; commit message:

The default kind of wrapper had changed to script-only in plugin 3.3.0. Also pin the plugin version to avoid unexpected surprises in future.

I assume there was an increase in reported failures after the wrapper switching its default behaviour from bin to script-only which was addressed by ensuring bin was used in all cases. The "autobuilder" is just a best effort approach, consisting of many heuristics to try to successfully build as many projects as possible. Note that the default switched to source-only quite recently (April 2024), so using bin is probably still the best choice for most projects. In the future the balance will likely tip in favour of script-only once more and more project start relying on it.

Yes, the autobuilder assumes that if no maven-wrapper.jar is present then this may be because we are expected to acquire the jar ourselves somehow (often because we're working with source-control rules that don't allow storing a jar in-repo). However it doesn't recognise the augmented mvnw script that can do the download itself. It should at least be harmless, if a little annoying to revert what it does when working with a persistent checkout of the repository.