The downside is if a product no longer have maintainers you are now encouraged to shut it down, even if it still works and it doesn't cost much to run.
If a product non longer has maintainers, it's probably because it's not worth it for the company. So it makes sense to delete it, from the company point of view.
In that case the product should still have maintainers. Even if only part-time, no software project should be completely unsupervised.