Why don't all cellphones have extendable antennas?

If his was not extendable, would Mr. Kim (engineer who died lost in an Oregon forest) have benefitted by a cell phone with an extendable antenna?

I would rather keep an antenna retracted but have it extendable when needed.

Could it make a difference at 1900 MHz, or is it only effective at 800 MHz?

While driving red lights and siren in Denver, we must notify law enforcement agencies whose jurisdictions we will travel through.
After clearing through Aurora Police Dispatch, next I call Denver Police dispatch usually while on Havana St.
Before an extendable antenna, my calls would often drop in that area.
I'd call back, usually getting a different dispatcher, and have to start the whole process over: (license plate, make, model, year, color of vehicle, route, destination, call-back number, etc.)
With the Motorola E815 extended, we have not dropped calls in that usual area.
Coincidence, or does the antenna extended help?

Thank you,

you must realise that extendable antenna might be usefull to you, but it's useless for 98% of cellphones users...so they can't built all cellphones with extendable antennas...

Yeah, I've never seen much of a difference using an antenna.

I don't like any kind of antenna on my cell phone, it just makes it harder to get it out of my jeans pocket.

Not sure but I don't think it would make any difference or maybe barely noticeable difference.