Only because the ISP's made it that way. Having 1Gbps down and 10Mbps up. You are forced into consumerism of bandwidth instead of a peer. ISP's don't want competition so you'll never be a peer.
I don't know about cable, but I suspect it's the same there.
OTH, fiber-based internet often has symmetric speeds. Don't know the stats, but I suspect most fiber ISPs gives you that.