"Kirk to computer, lock onto my position, scan the alien hieroglyphs around me, run them through the universal translator, and read them to me. Also, let me know if any lifeforms are approaching". Bam, easy. Wonder why the writers never thought of it.
Don't think about it too much. Generally speaking, original Trek (and TNG) were full of more plot holes and inconsistencies in a single episode than the two JJ Abrams movies combined. (Not that the haters would ever admit that, of course.)
Short answer: Because they didn't have the decades of experience with computers that we have now. Long answer: Think of all the crap people do on their smartphones today, how much of it did you imagine people doing when the iPhone was first announced? Some of what we do with them is obvious, like surf the web, texting, and making phone calls, but other things, like using the camera to take photos of an object, when are then processed by the phone and sent to a 3D printer so you can print out a "copy" of the object would never have occurred to you. That only came about because of all the people who got their mitts on the technology and played with it to see what it could do. If you haven't watched James Burke's "Connections" and "The Day the Universe Changed" series, which detail the strange paths technological development takes, and the impact it has on society over the centuries, you owe it to yourself to watch it. The end of the first season of "Connections" scarily predicts the sorry state of politics in the world today, and it was recorded in '79! We're also blind to the capabilities of technology in the real world, even when we're dealing with technology that you'd think we well understood. For example, the steam engine was invented in the late 1700s, and metal workers had been using bellows to get hotter fires since the dawn of time practically. It wasn't, however, until almost the 20th Century, that anyone figured out that if they increased the airflow through the fire box of a steam engine, the engine would run more efficiently. The technology to do this existed almost from the beginning of the steam engine, but nobody bothered to apply it to steam engines until about the 1880s. If I, or someone familiar with steam engines, were to walk into a locomotive factory in 1861, we could find all the parts we needed to increase the efficiency of the steam engine dramatically, all sitting on shelves, but nobody from that time ever thought to put them together in the way needed.
Hell when Star Trek first came out, half the stuff below didn't exist. And now, you can buy something the the size of a deck of cards that does all that for $50. But even 10-15 years ago you wouldn't believe that a smart phone could do everything below.
There seems to be a long-term oscillation between centralized and distributed computing as hardware and communications costs drop. The first computers are very expensive and communications are poor/non-existent, so if you want to use a computer, you go to where the computer is. Then the hardware gets a little cheaper and the communications get a little better, so you get terminals spread over a building, campus, etc. and you do your work far from the actual computer. Then the hardware gets a lot cheaper and the terminals suddenly become computers themselves (PCs), and the central computer, if it's needed at all, is used mainly for data storage. Then the communications get good and cheap, and the PCs become glorified terminals once again (WebBooks, etc.), with all of the applications being run on a remote server. Then the hardware gets a lot cheaper and smaller and the communication becomes wireless, and we all start carrying 1GHz processors in our pockets (smart phones). Fast forward to the 23rd Century... The communicator (the descendant of today's smart phone) has computing power equivalent to 50 million Pentium processors and enough non-volatile memory to store every bit of data generated by the human race. If it has a multitude of sensors--undoubtedly good, fast, cheap, and small in the 23rd Century--then there's no reason why the communicator and the tricorder can't be the same device. Sending voice (how quaint) messages to an orbiting ship will be, like a modern smart phone, one of the least impressive things it does. Oh, it will also run for 50 years on the energy from one snap of your fingers and it will be connected directly to the sense and memory areas of your brain. COMMUNICORDER!
Being able to send text messages would be really handy in certain situations. Kirk's communicator seemed to be incapable of sending Morse Code.
Or even what a phone can do now "OK Google. Send a text to (person) saying 'Come get me from (store) at 5:00 pm.". Which can be "Ensign Ricky to Enterprise, emergency beam out now!"
