My assumption for reason that old noise releases are so long, was mainly that stores were selling C-60 and C-90. So bands and labels put out tapes of those lengths. C-45 were way more rare to find.
As soon as shorter tapes were easier available, there were being done.
I am not particularly fan of C-10, although I appreciate 7" a lot. It is perhaps because there are TONS of good 7"s, where artists put great track on slab of vinyl, yet C-10 is often treated differently. Especially at some point, it seemed sort of disposable format. Quickly dubbing small run to having "something out" for gig or latest batch, not that it would be standing out like 7" material might. Of course there are exceptions.
However, like someone pointed out, it may be quite old discussion now. Who is making C-10's? It had it's peak in over 10 years ago, and at this moment, barely existing thing?
For live music culture, diy, face to face interaction, special packages, etc. perhaps very much suitable format. In international mailorder thing, I would guess that most people will conclude that they aren't paying the money that it nowadays costs to buy AND ship tape, and get just 10 minutes. Regardless is it good or not. You can get bunch of good, and perhaps better releases for same money.
For me, C-20 is already perfect length of tape that is not meant to be "album". For a lot of noise styles, that are more structured or hectic, length may be perfect.
