Manuals in PDF format

Manuals are one of the vital things of the IT field, the source of information about how to handle certain programs and problems. Surely they are not always top, but always better than nothing if you are able to read them. Sadly it got to be a common habit doing them in PDF format by now, which requires an external program for viewing - the Acrobat Reader, which does not automatically come with the operating system. Why the heck do they that to us?