I'm not the most tech savvy guy in the world, so I'm certainly willing to be corrected, but my major problem with SSD's is this: when they fail, they do so without warning, and in a way that makes even partial data recovery impossible for an average user. On the other hand, in the decades during which I've used HDD's, I've never once had one fail without giving me some kind of warning. The dying drive has either overheated, or started showing read/write errors, or made distressing noises (kind of like that death speech all the soon-to-be-croaked best buddies get to make in action movies). And I've even been able to recover at least some data from drives that were seriously screwed. The only failed SDD I ever dealt with simply didn't report on boot, and I never heard anything from it again. So to me, a big SSD just offers a better chance to lose everything all at once, minus whatever was saved in the last backup.
And then there's cost, of course. I just bought a 2TB HDD for eighty bucks. I know I won't be seeing any SDD's available at that capacity/price for a long, long time.
Right now, my ideal computer would have a mid-size SSD for the operating system and installed programs, and a big, fast HDD for most storage needs. And, of course, my external backup drive would use old-fashioned platters. I'll leave huge, relatively expensive SDD's for those whose need for speed is much greater than mine.