Why is US Broadband so slow?

It's so much more subtle than this. Regulation is great, but I'm not sure you can attribute the speeds you see in foreign broadband to that alone.

In the quest for "balance" between public and private interests, the Telecom Act of '96 created a scenario where carriers still "owned" their network, but had to share access based on a set of rules. The problem is, everyone who came to play still had to use the same old infrastructure.

The RBOCs weren't stupid. When it came time to upgrade the infrastructure, they came to the table ready to negotiate. Because they knew the voting public would never accept a publicly built and owned nationwide fiber optic network, the carriers negotiated incentives so ridiculous, they almost sound like a work of satire.

Cable companies managed to avoid the regulation hammer altogether, but have consistently "out innovated" the telcos. I use that term loosely, but when you're studying regulated vs unregulated, it's pretty easy to see that unregulated "won" here in the US. Unregulated didn't really win though. The regulated model we use here in the US is flawed.

When carriers are forced to share their privately owned infrastructure, the incentive to upgrade the network goes away. The US is too large, and land-use rights too difficult to navigate in order for there to be a competitive market.

I believe we'd be much better off if we were to adopt a model not unlike our national highway system. All the fiber would be laid and owned by the public. Regional tandems would work just like they do now, but would be publicly owned facilities. Private carriers would pay for space at the tandem, but anyone is able to come and bid at auction, similar to the way spectrum is auctioned off. The incentive to keep the infrastructure up to date would be driven by voter interest.