It's unnecessary and expensive. And the vast majority of people don't care too much about their upload speed.
If you truly need symmetric broadband, you can get it. It won't be cheap, but it's available. Call your telco and ask them about leased lines.
Most installations download way, way more than they upload - especially since people are ditching their TVs for Hulu, Netflix, and Youtube. That's the reality, and companies have built their installations to match predicted usage. Right now, most traffic on fiber runs from the internet to a consumer. Making everything symmetric would require either slower speeds or more fiber, more equipment, and more money.
And really, the only advantage symmetric gives you is the ability to run servers, which is against most consumer broadband terms of service anyway. I violate the TOS and do it anyway (for personal use), but if I wanted to run a real service, I'd get hosting or CoLo.