Most people don't need 1Tb of space, let alone 2Tb. It encourages data-hoarding and ultimately, loss. If
you "need" so much space it's because you're treating is as your
primary store and not a window on it. What you should be doing is using
the cloud and only using what is current. Whether it's music, photos,
videos or whatever - it should be on cloud storage to be safe. Even a
backup at home is not safe.
The trouble is, most users, if not all, do data hoard. Especially home users. They'll have ten years of family photos on there, their music collection and quite possibly downloaded films. You can't change user behaviour easily and the current requirement is for more storage, not less. The sensible ones will back it up to some sort of cloud storage but you also have to bear in mind a lot of cloud services sync the data (dropbox, livedrive, etc.) and keep a local copy thus you still need the disk capacity.
A decent sized fast SSD is the exact same price as a large but dog-slow
5400 RPM HDD so it makes no sense to "make do" with something 20x as
slow when it's going to cost the exact same amount.
In the real world it's nowhere near 20x as quick. I've got a 1TB SSD in my work laptop and yes it's quicker booting up and a bit quicker to open apps, but 20x? No way. The bottleneck in system speed isn't always the disk.
Most sensible people buy the best option that they can for the money, I
can't understand being willing to buy something that's slower but costs
as much.
Because a larger disk may suit their needs better. You have to remember 95% (if not more) of the PCs out there are still using normal hard drives and getting along ok with them. As the capacity of SSDs grows and PCs get replaced then the industry will migrate across. Yes, that's a good thing but don't expect the user to suddenly go 'wow, isn't this wonderful'. We'll still get the same grumbles about slow apps, slow internet etc.
"hey, they didn't have the fast car I wanted but I got this tractor for
the exact same price!! I don't mind that it takes me an hour to get to
work, I'll just drink coffee".
Because they might also want to plough a field. ;)