If it's not clear, in the US, only the top trim has factory installed parking sensors. However, on all other models, it's possible to get dealer installed rear parking sensors. I've been asking about the latter, since I really don't want the turbo.

 

So they would have to replace the bumper which won't be cheap ( or drill the holes) It would be better if they just put them on every car at this point and price point.

 

I believe they drill holes. One of the third-party official Mazda parts sites has the instructions. It's fairly intimidating - not only removing the bumper to drill holes, but removing the interior panels to thread the wires and install the optional switch (necessary if you ever pull a trailer, or maybe even a bike rack).

I agree with your conclusion.

 

The don't replace the bumper.

For techs that do this all the time, it's not intimidating or difficult. It's just another job during the day.

It all comes down to money when building and selling cars.