All roads lead back to about half a dozen companies. The concentration of power is astonishing and terrifying. They have all of the US, maybe even the world, checkmated. Nothing good will come from this.
There are literally thousands of web hosting options; Parler can go find a different one.
The minute you force a company to do business with people they don't want to do business with is the minute you've nationalized the business. So that's the solution -- if the US government so strongly believes that these resources are vital to society in the way that, say, the electric grid is, they need to turn them into regulated utilities. Until then, they are profit-seeking companies who believe they are protecting their shareholders by choosing to refuse service to a customer.
We still consider power companies a monopoly. It doesn't matter much that some alternatives exist if they are so inferior.
And from a practical standpoint, depending on how _much_ power you need there may be no other way to get power to your property besides the grid.
None of that applies to Amazon. For every service they offer, there's an alternative available.