well, the thing is that hdd's keep getting faster and bigger too. 100 bucks buys you 3TB. for 300 bucks you can get 9TB.
That's true; OTOH for personal use, there's often no benefit to buying more capacity since you won't be using it anyway. For example, my disk usage never reaches the 250GB mark, so for me there is little point in paying for more capacity than that.
Which means my choice is between a dirt-cheap (but slow) 500GB spinning disk, and a not-so-cheap-but-still-affordable (and FAST) 500GB SSD, and since I don't like waiting for my computer to do things, I'll choose the latter.
As both SSDs and hard drives get cheaper, my next 500GB drive of choice will be cheaper yet; the fact that I could buy a cheaper and/or larger spinning drive instead doesn't matter much since then I'd have to use it (zzzz)â¦
Other people will have higher thresholds, of course, but as the technologies mature they'll reach a point where most shoppers will find that any drive's capacity is "sufficient" and then their choice will depend solely on performance and price.