Thanks for your answers guys.
If there's enough market saturation of their product, the bad guys will be motivated to produce their own exploit. And by releasing a patch, they pretty much have what they need to do so. Taking the company's logic one step forward, if the company feels that their user base isn't technically proficient enough to patch (as the original poster stated) AND the patch might provide enough detail for an attacker to develop their own exploit, should they have even release the patch?
And this is exactly the problem! Most of my found vulnerabilities might be easy to reproduce for an attacker, even if they only state the type of the vulnerability in their patch notes. So patching it silently might be the right way here. But the problem will still persist on the devices of the people who simply cannot update due to a missing technical understanding. If the devices would auto-update, this wouldn't probably be a problem, but this is not implemented for some reasons.
So the vendor doesn't like to see the vulnerability to be disclosed because of loosing reputation and of course to protect their customers in the obvious "security through obscurity" way.
@3xban:
I had a talk with the product manager again about the situation and he clearly stated that they appreciate all of my further findings too.
I finally agree with unicityd - if and how they report this issue to their customers is their descision/problem, so I decided to take their offer.
Regards.