In most of the country (at least in the US) you are rather limited on broadband access. There is typically a cable provider in the area, and many of them do not offer Internet access. There is typically a telephone provider that can provide you service, but even the big ones don't offer Internet access everywhere. [I live in a city-burb of Chicago, in a high-end neighborhood, and though I get dozens of leaflets from AT&T every year about cheaper, faster access, they don't offer it at my house. Go figure.] So most people in the US don't necessarily have a lot of choice.
The second piece of this is that if you want to always pay the cheapest rate, you're going to get shared, multiplexed service. If you want dedicated bandwidth, it's probably available to you. Just ask for business class service, which will give you a guaranteed rate. Of course, you're going to pay significantly different costs for guaranteed rates.
Finally, you have the option to complain as a customer to your provider, and to rally support with other consumers. Do it. Meanwhile, *everyone* knows that home Internet service is a multiplexed service, even if they don't know the term. It's like your subdivision street. Your provider will gradually increase bandwidth as the "street" gets busier. However, it makes little sense to invest $100,000 in a vault upgrade or add a $200/mo charge to their operation when 98% of a 100-home subdivision is barely using the bandwidth, and 1 or 2 users are constantly consuming all available bandwidth. They should pay for the upgrade. But they'd rather complain. The provider's obvious option is to shape them. Most of the time, that just means lowering priority for certain classes of traffic such as file sharing protocols (Gnutella, eDonkey, etc.) compared to interactive protocols such as http. Few bother to do rate limiting. Mostly, they just shape so that when the network is operating near capacity, the interactive stuff gets priority.
Meanwhile, no one else wants to bear the cost burden of increasing bandwidth just so Joey-down-the-block can share files with his buds across the planet. If my provider told me that they have to increase the costs in our area because Joey's complaining, I'd laugh and tell them to charge Joey.