Cost of DMS prohibitive for OEMs31 Oct 2020 15:15
Very rarely if ever will an OEM incur cost for safety features before they are mandated or legislated. Reversing cameras are a good example - even at a total additional cost of around $20, most cars didn't include the features until it was mandated a few years ago.
The safety star rating system through NCAP has been the most successful way of promoting the inclusion of safety features, but NCAP know that they have to let the OEM some control over the place of deployment. A basic DMS system, that works, is still over $100 USD making it much too expensive.
There's an old saying in automotive, safety doesn't sell cars, sexy sells cars and hands off wheel is sexy, but cost still limits the feature to higher end vehicles at this point in time.