/sigh
You have to look at the big picture, and consider that the majority of this is a matter of the law's steadfast refusal to change and adapt to the times.
Consider:
Copyright law was originally created to protect the small, independent creative person from the big, scary, large group of singular individuals that would take his creation and use it as their own for whatever ends they might see fit. Since the laws can't apply to some and not others, this law applies to everyone. That includes large powerful corporations that it was, most assuredly, originally conceived to protect people from
Consider:
WotC is a large corporation that owns the rights to a very popular piece of intellectual property.
Do they care about taking that property and turning it into something in line with it's creators vision? No.
Do they care about molding it or shaping it into the most perfect, visionary, amazing system ever seen? No.
Do they care about doing what is best for the property, such as willingly putting it in the hands of someone who does want to do these things? No.
Do they care about the intellectual property at all? No.
All they care about is making a bunch of fucking money.
Most importantly... do they care what you think about them?
No.
Because you will buy their product anyway, no matter what you think.
Because if you obtain it without buying it it's copyright infringement, and they will sue you.
The idea of downloading older books that WotC no longer supports doesn't work because they still own the rights to make their money off that property.
It's the "potential market" clause that Maat tried to point out.
The act of downloading an electronic reproduction of something is considered the same as if you had reproduced an exact physical copy of it.
All they have to do is drag you in front of a judge and say, "Well we were planning on re-releasing these books at some point and now due to his unlawful reproduction of our property we are unable to profit from it."
And then it's game over.
Even you turn to their lawyer and say, "Orly? You were really, truly, planning that? Swear to it? In a court of law?", that lawyer could just shrug and say, "Whether we were, or weren't, or could have might possibly maybe potentially would will have been might be maybe was something we were or were not planning at some time in the future, now because of your unlawful actions we won't be able to. Give us your money to make up for it."
That's pretty much it. They can do whatever they want with their property, for no other reason than the law is on their side.
As long as it will make them some money, they'll do it.