Something like that would have(and has) very strong resistance from doctors,which have a lot of influence on the healthcare system, turning them(to some extent) from highly respected, smart professionals with a lot of autonomy and responsibility, to cogs in a big machine .

Also such system is quite complex in many dimensions, so the natural risk minimization strategy would be to introduce it in stages: a system that warns about drug interactions here, monitors drug dosage there, reminds you to order extra tests, etc .And of course everything needs to be clinically tested to be accepted by docs(even though it isn't stricly necessary, it's just a second opinion, reminders, not the final word) . It makes for a very slow process.

And they they all face very big adoption barriers , in some cases upto 96% of their recommendations are skipped. Some of this is due to usability , but a lot due social/political factors.

Now after seeing this, what company in it's right mind will invest in developing a full diagnostical system ?

Actually , i know of one who did, http://www.isabelhealthcare.com , but at least according to the founding story , it began because the founder nearly lost his daughter to a hospital misdiagnosis, so he wasn't really driven by money.

And as far as i know(haven't followed them in a long time), they only achieved small scale sucsess.

The other company now entering this is IBM , but that's a bit of a unique case: IBM may be in big trouble so they take a huge bet, and the field they choose - cancer , is such that patients have much more power than usual , a patient has time, and can demand a diagnosis by Watson , heck it's even a cloud service, you just need to send blood and pay.