They are all counting on you not using all of that space in the 2TB plan. So the avg user is subsidizing the usage of some small fraction of power users. They don't want to offer pay-per-use pricing plans because then they would have to increase the price ($/GB/month) to keep their existing margins.

This is one of the very techniques under which the entire Apple Empire has been built. They take the "sweet spot" for $product and intentionally offer options on either side of that sweet spot. They also nerf the lower-end option in other ways (i.e. fewer ports) so to make the upgrade more enticing. This enables them to offer "Prices starting from...." that are dead-end options (like 8GB RAM or 128GB HD's).

Lots of companies do this across various industries. But it works best when the brand name is really strong and/or the competitive landscape is very weak.

I've grown to accept that it's just how they operate.