Every time someone replaces their starter motor and moves the intake back or fully pulls off the intake, I never hear of them proactively replacing the crankshaft sensor which is right there.

With all the work you are doing to get to the starter motor, why not replace the crankshaft sensor?

Next:

When your 5 series doesn't start, I never hear of anyone examining the on/off push start button for a broken button or the brake petal switch that makes you depress the brake to start the car. Since both switches get a lot of use, It seems that both of these switches could be prone to breaking, but I never hear of anyone replacing either of them. What's up with that?

 

I like the Idea of replacing the sensor. Cheap and easy to do.

There is a big difference in "won't start" and "won't turn on".

No reason to troubleshoot the brake switch if the brake lights turn on.
No reason to troubleshoot the push button switch if the car turns on.
No reason to discuss any of those in a forum post about a possible starter motor problem.