Haha, funny you think they care about catching someone robbing you. They are selling cheap cameras to uneducated buyers.
It has a very small data cap; only enough to send compressed files (think kb text files, not gb video files (it has a 80 kb transfer cap, with 500 mb monthly total cap

.
It currently seems to be in the testing phase, but the system could be setup to be a backup connection for their analytic data collection; so they can market to you better and sell that information to 3rd parties. If an Amazon device loses internet connection, this program will allow the tracking algos to continue to phone home and deliver it's data by piggybacking off of a neighbor's Amazon device.
Wild speculation territory:
There are also other, future options to track people, especially if Amazon tries to break into different markets (and finds ways to get people to carry an Amazon device with them, at all times). Over the last few years, part of Apple's marketing strategy has been to push protecting privacy from the more invasive 3rd party tracking apps. This Sidewalk mesh may be part of a plan to circumvent the date gate-keeping that Apple and Google can implement at any time.
For example:
Apple could totally disallow any app from using the GPS data (currently a user option), while still allowing the app to use wifi (since most apps need wifi/5G to work). As the phone is traveling, it is looking for Sidewalk IDs, that uses the home/business IP to get a location. This would be more accurate and use less computer resources than using the cell towers to triangulate. This allows them too see what stores a person is going to, and then the algo can try to steal that business away and send it to Amazon.