There are solid reasons for bundling items, although the intention is not to allow the buyer the most granular customization possible at any cost.
If enough people bought or ordered option-less vehicles and purchased the desired parts to effect an installation of the options that are instead desired, you can believe that they would alter their marketing mix via the equipment in the bundles. It's no longer the muscle-car era of car retailing, and this just doesn't happen.
As it is, the options for the B Class are relatively inexpensive portions of the entire purchase price, so it's less inhibiting than it could be to simply add each package necessary to contain the options that you do want (as well as some that you don't particularly want.)
I have had serious reservations for years about accepting a vehicle with drivers' rearward vision so restricted such that a camera was even desirable, and if I've got complaints about the camera they would have to do with the vehicle even needing one. When it came time to decide whether or not to include it - no contest, we got it, despite the entertainment system package that I could argue isn't an upgrade worth having.
In this region, the Mercedes Benz dealer was the first dealership of any brand that we visited that would entertain the idea of searching for or ordering a car with our desired specs and equipment. The fact that ours was a lease decision made it a bit more acceptable to choose one from existing inventory that was fairly close to our wishes.