Well, they do: Doctors and other medical professionals have come to rely on cell phones to be notified of emergencies quickly enough to save lives. If they are blocked, there's a realistic chance lives will be lost for no good reason.

(I've never heard of a good reason to block cell phone transmissions. It always seems to come down to trying to enforce some vision of politeness via technical means, which doesn't take considerate cell phone usage into account at all.)

This is why it should be possible for theatres and the like to set up alternate base stations that cell phones connect to, this way 911 calls and text messages incoming may still be delivered but no incoming/outgoing calls may be connected.

In the scenario I'm describing, the doctor is going to the theater when they get a call from the hospital saying there's someone there who needs their skill. (It's actually in their contract that, while they're on-call, they have to remain within a certain amount of travel time from the hospital so they can get there in time. This does affect home purchases.) If their cell phone is blocked, the call is missed and someone may very well die.

You could (presumably) attempt to fix this with technology. It might even work for a while, but when it breaks, someone could very easily die. And they'd have died of someone else's dislike for cell phones, which is not a good reason.