It's a (underfunded) government industry - change often takes a lot of time in big companys, especially with their high demand to security and procedures.

I'd like to recommend the AVWeb series "Say again" series by Don Brown. It gives some insight in the last decades of the airspace controlling government industry and it's problems.

Example: http://www.avweb.com/news/sayagain/182641-1.html

Probably just that interactive text conversations have become "native" only recently.

My mother more or less refused to text up until 4 or 5 years ago. It had more to do with the totally novel paradigm than with any piece of the technology used to implement it.

It also has to do something with radio (voice) frequencies beeing at max capacity in high traffic areas.