I don't see any mention of 'shitty', just over-engineering. For the record, I would use Vagrant if I had the need, and probably will in the future (this kind of caveat seems sadly required otherwise I would be painted as somehow opposed to a software project), that said..

Fitting in with the community style/idioms is rather important for a project, especially as it grows in size. When it's a huge codebase, used by many, in many different use-cases, people being able to look into the code to help sort out their own issues is hugely valuable. If someone who knows your programming language and knows your problem domain gets scared off by how your software is architectured/functions, that's not a particularly good sign.

But maybe the problem is huge, and all that complexity is needed, and will pay-off now they're looking to have multiple VM providers. But criticism of complexity shouldn't just be tossed aside as 'trashing'.