@amerika >What is the law you refer to in the first paragraph?
Copyright law forbids the sharing software unless you have a license to do so.

Free software licenses like the GPLv3 and AGPLv3 etc do give you a license to share the software mind you.

>In the 1980s, there was software available for mainframes... much of it free and in source code format.
Yes, originally pretty much all software was free and provided in source code format and could be shared freely, as copyright didn't apply to software.

Businesses then started to refuse to provide source code and then copyright law was modified to suddenly apply to software and businesses quickly exploited the created monopoly.

>You can still distribute software this way without a license.
Software without a license on is placed under the default "All Rights Reserved" terms by the government, which makes it proprietary and unable to be distributed (the one exception for this is if it has been validly placed into the public domain, which is very hard to do).