It's not being throttled. There is a peering dispute between netflix's CDNs and the ISPs. Netflix's CDN's don't want to pay for delivery to the ISP. Normally CDNs peer with each other for free if the balance in each direction is equal. The problem is that any CDN that delivers netflix is hugely unequal since it's a huge one way stream.
The ISPs could just eat the cost, and let it be delivered for free. Or Netflix's CDNs could just pay the peering fee. Or Netflix could use different CDNs.
The reason the VPN works is because it sends the data over a different CDN that isn't saturated because of the dispute.
At least that is how I understand it, but I'm not an expert (or even a novice).
Umm wait, isn't such a dispute exactly what we call net-neutrality? Consumers pay ISPs for internet access, and now ISPs also want money from websites that provide a service to the consumers. But filtering those websites until they pay the ISP to be let through is the opposite of net neutrality. If what you're saying is true and ISPs are asking Netflix (or subsidiaries) to pay them to be let through unthrottled, then this is indeed the net neutrality problem as the OP reports.
Edit: Wait I think I understand. I messed up peering and ISPs, right? Because the CDN connects to the internet via peering, and they're charging money (which does make sense to me), not the ISPs.
The ISPs could just eat the cost, and let it be delivered for free. Or Netflix's CDNs could just pay the peering fee. Or Netflix could use different CDNs.
The reason the VPN works is because it sends the data over a different CDN that isn't saturated because of the dispute.
At least that is how I understand it, but I'm not an expert (or even a novice).