At present, CMS Collections can only be placed on one folder off the URL. See example:
This may not be an issue for a simpler website, but let's say you have a website structure that may warrant something like this (bold being the CMS collection):
mywebsite.com/project-item (making collection a root slug)
It is simply not possible. It makes it really awkward for both site structures internally, and also to be to achieve succinct, easy to understand URL structures, externally.