Assuming incompetence before malice, I'd say that Qualcomm and the other 5G baseband manufacturers have such a moat around cellular modems that it doesn't need to be secure. It's not a competitive advantage. A security critical application simply assumes that the network and the 5G baseband are compromised.
So, security itself is driven by third party organization(s) that consists of engineers from mobile technology companies. If Qualcomm wants their cell modems to be 3GPP certified, they _must_ comply to the 5G standard in it's fullest, including all security features (the same will be true for future revisions, 6G, etc)
There's also groups attempting to make mobile protocols and provisioning entirely open source (O-RAN) which, ironically, will likely improve mobile protocol implementation security practices as they can be audited by anyone with an internet connection.
You may be on the right track here. It's just one anonymous HN comment [1], but it fits other pieces (e.g. BSP code dump quality).
The sad thing is, there is no competition where one could go to - it's either Mediatek who have serious issues of their own, or Samsung who mostly stick to themselves.
I know they're proprietary, but got any more info on this? Would be super interesting.
I remember a pretty egregious mis-implementation in a qualcomm rsa encryption module many startups ago when I was using that, I never heard back about the bug report.
That was over a decade ago so surely it's fixed by now I guess. I guess?