You forgot no fun to grab of when it's really hot or cold out

Set one down in the sun for a couple minutes in the desert at 115 degrees and pick it back up, you'll only do it once. I have some Ti handle knives I really like and carry/use frequently in the office or the house, but when I'm out in the elements doing field work etc. I gravitate back towards a knife with a textured handle on it that actually provides some grip. Very very few Ti handles provide good grip, especially when wet or with sweaty hands over extended use. Most people use a folding pocket knife very little, they might use it once or twice a day to cut one thing. So for them things like grip, comfort in extended use, etc. don't matter. Knives are becoming like watches, more fashion than function and the knife industry is responding to that.
There's a few advantages to Ti, it's light, and very durable. Also it's efficient in manufacturing, you can build the handle and lock out of one slab, less screws, no scales, no liners etc. etc. I don't know if that offsets the higher cost of the material but it's certainly more efficient, and there's something to be said for less moving parts etc. I'm sure it allows "cleaner" looking designs with less parts.
I think the real popularity of Ti is that customers have a notion that it equals high quality and exclusivity, call it the unobtanium factor. Carbon fiber is exactly the same, no real advantages over G10 (and some significant disadvantages) but it's all the rage because of aesthetics and fashion.
Also Ti handle knives typically mean it's a frame lock, and while it's a perfectly good lock if properly done, it's very hard to do right and even harder to do right mass production. We can barely get by a day here without seeing a new post about a bad frame lock from even the most respected manufacturers.