you know that type face was invented for print. it's clearly a lot more efficient to mass produce a printed work by mechanical typing than hand writing.
I would assume that since people have variable writing styles, some that are hard to read, typing acts as an equalizer and allows uniformity in writing formats (apparently that is a good thing) and I suppose that it just seems more proffesional.
people have been typing for so long, and since everything is computers today, people now type far more than they write by hand, if they even do at all.
Also many people (myself included) can type at a rate about 10 times as fast as I can write anything. And the few times I've tried typing on a touch screen protoype (pre-iPhone) it was slow as hell.