Why has digital technology become the most reliable state of the art technology for data and information storage and transmission?

It isn't.

If you print something on acid-free paper, it will be easily readable in 200 years.

A harddisk, on the other hand, rarely last longer than 5-10 years even under the best conditions. A CD or DVD may last 50 years, but no one knows for sure yet.

Even putting physical reliability aside, it is not at all obvious that the programs we use in a few hundred years will be able to read the data formats we use today.

Compare to punched cards: They were a primary digital storage medium as recently as 40-50 years ago, but you will be hard put to find a punched card reader for a computer bought today. And possibly even harder put to find software that knows what the data means, especially for binary data.

Digital technology has its big advantages in operating on data - whether summing or copying, the computer is much less likely to make errors than a human - and in searching. Finding anything specific among millions of printed pages can be a hopeless task, while searching the same volume of digital data is trivial.

Digital technology has several massive advantages, but storage reliability is not one of them.