On the down side switches are expensive and can fail though so they add warranty cost and another 'hole' in the case.
That said, a phone case that covers up all of those bits until you expressly open access to them would probably sell well.
We already have good enough technology that a phone should last us 10 years at least without having issues with the performance. The only problem is having replaceable batteries.
We need to move back towards things that last and backwards compatibility. Then it would make sense to pay $1000 or even $2000 on a phone, since you know it works perfectly and it'll last you 10-20 years.
Uh, no they aren't.
In addition, since switches are an electromechanical component, they also affect your mechanical case engineering which electronic components don't do.
Finally, if your device is "water resistant" or somesuch, you now have an even bigger engineering headache waiting for your design team. Especially since you don't want a pushbutton, you probably want a slide switch.
Switches and buttons are really expensive on electronics components from a relative cost and engineering cost standpoint.
The easy way to ensure that a switch is waterproof is to use something like a magnetic reed switch or hall effect sensor, so the switch just moves a magnet, which is sensed thorugh the plastic case. It uses more real estate than a pure switch, but requires no open holes through the case.
This is at odds with the (apparent) consumer preference of smaller everything.
Um, using a hall effect sensor is exactly the kind of "soft switch" we're trying to avoid, no?
And magnetic reed switches are big, very expensive, vibration sensitive and failure prone. Since this is security, you're going to want it to fail open and you're not going to want a switch that closes briefly if you vibrate the phone.
Mechanical engineering is hard. Let's go shopping! ;)
Reed switches are available that are a few mm long, they aren't exactly huge.