In principle, I think it’s good to have many channels through which resources can be accessed, but I also see reasons that speak against it.
One obstacle would be whether the respective creator or the license of a resource allows this. Another reason would be that obsolete versions would circulate in the net. And I’ve seen at least one repository on GitHub from which the resource creator basically removes old versions when he publishes an update of his brush pack, since he apparently doesn’t want to do that, but not everyone does that. I know something similar from resources on Deviant Art and GumRoad.
I would imagine that authors want to avoid service debacles this way.
If someone came to me and said, “I just downloaded your “Big Brush” preset, and it just creates incoherent blobs when I paint,” and I thought I fixed that exact bug with an update, what the hell did I do wrong again, I’d probably be looking like a maniac for a cause, since I haven’t authorized any other distribution channels to rule out just that.
Wouldn’t it be better to create a web page where you list all the resources you know of and provide links to the respective download pages? Something like the manual, but you could also present the resources, maybe show a tally mark for each preset, or something. I’m sure there are many ways to present resources and provide access to them.