I'm sure it must be nice for pilots on a hot day to pop open their windscreen while waiting on the tarmac, but is there a good engineering or safety need for them? There must be a significant amount of cost and time effort in making a windscreen both openable and safe. If the pilots really need some fresh air, they're usually pretty close to the passenger door.
I can imagine there were valid historic reasons for having them: when planes were smaller and instrumentation not so sophisticated, you might literally want to take a proper look at your propellers spinning before setting out. But why do we persist with them?
737 Max with both its cockpit windows open source
Airbus A380 with open window source