Well, there are good answers that explain how various simplifications and improvements were already implemented in various instrument designs. That's true. Same goes for the notation, just look at the history of its evolution. I also want to agree and confirm that the mental abilities required to play music can only come as a result of a lot and a lot of practice.
But also I think you are interested in asking a different and a more exact and practical question:
Why are not the classical instruments made as much easier to play, as requiring only about a year or even less to master?
And I want to question your premise on this one.
A classical musical instrument is all about making a complex physical medium emit a particular characteristic sound in a very controlled manner. And the simple answer to why this cannot be simplified is because you can't avoid dealing with the particular physical configuration of materials that comprise the instrument.
There are hundreds of ways of plucking a guitar string, there are hundreds of ways of pressing and releasing piano keys, there are hundreds of ways of closing a pipe hole with a finger.. Every tiny detail of every movement of the hand contributes to exciting the physical medium into producing the particular sound with particular details. Every movement should be performed at its exact timing, lead by intuition, without additional time for consideration, and with connection to all other movements. Otherwise there will be no music.
Building your control over this to an extent suitable for playing music that can be enjoyed by other people requires a considerable amount of practice and training. Your hands, your brain, your ears, your posture, everything must be trained.
Physically, playing a classical musical instrument is a dance, and you probably won't question why dance is not being made simpler. Or shooting from a classical bow if you are familiar with that, or fighting with a sword, or learning kung-fu.. it's art.
Also, changing a guitar or a piano, would make it to be not a guitar or a piano anymore. They will sound and handle completely differently.
In your analogy with a car, I would note that playing music is more akin to professional driving like rally, drift, Formula-1 or similar kinds of it where a driver is expected to be able to control the car on an immensely vast spectrum of possible situations and to be able to have a working mental model, prediction and analysis of what is going on. Driving in these kinds of sports takes years and years to learn. Even the typical daily life car driving experience in most cases is about 5 years until the person becomes a seasoned driver.
Learning things through practice is just how life works. You are going to make a much better progress if you accept this and learn to enjoy the process.
I am not sure how electronics or touch screen technology can help with playing classical instruments or reading notation, but if you have any exact idea on this, I suggest asking a more direct question like "why methodology X is not used to simplify playing instrument Y in the way Z", so you could get a more direct answer.
That being said, there are tons of learning material available today for almost any instrument. For example you can find wonderful people on Youtube who share a lot of information, experience and spirit. As well as approaches to learning and understanding musical theory.
About musical theory and notation: from my personal experience I can say that they are already simple, it's just rules and a simple script that you need to learn. Reading notes does not take years to learn, it's more a question of about a couple of months at maximum for most people. I must also say that I know professional musicians who have trouble playing from the notesheet in real time, so that is possible too.
If you can think of an alternative and easier notation, please post a separate question about it and it can be discussed, maybe something interesting can come out of that.
Besides that, reading notes is easy, but being able to understand what they mean and how the musical piece works in terms of its inner structure and countless details, takes years to get into.
By the way, there are constant attempts to invent an alternative musical notation, for example take a look at https://www.hummingbirdnotation.com/
And there are attempts to take a fresh look on studying musical theory, for example take a look at https://www.hooktheory.com/