I think you'll find there is the "we'll not bother preserving it because there are so many copies already (of which we have hundreds)" and the "Preserve every copy".
I've never, ever heard of "only software that is needed for preservation is the programming languages and operating systems that ran within the capabilities of the vintage computer you collect. Any type of software could then be produced.". Do you know how long it takes to learn a dead programming language on hardware no one (or very few people) have used for 20-40 years? It takes months to years to make new Commodore era games, just like it did then, heh.
I've never heard of it, at least from the museums, archives and game collectors. Who told you this?

The only problem is when it comes down to physical space, and some collections simply can't accept everything. In this case, since we have no major tested and reliable way of sorting digital copies of software (that I know of anyway), this will be a problem if people are of a "Bin it or donate it" mentality. There are some projects slowly working on some standards and solutions to making reliable, tested digital copies of software, but usually laws require the originals be kept
somewhere anyway.
They take a lot less space then actual hardware however, even old school tape, "hard disks" (literal ones), floppies, whatever are a tiny amount of space compared to most of the hardware, if you don't mind losing or compressing boxes etc. - manuals might be hefty too however.
If you want to donate such stuff, there's certainly places which will take it. Here's a brief list of
game places I maintain, but most are general computer software archives/museums too.