AG, that's because those cheap solar garden lights you got don't have proper charge control for NiCad's, there's nothing wrong with the chemistry, for heavy load applications it's superior to NiMh because the peak current you can get out of a NiCad cell is significantly higher than you can get out of a NiMh. This is why you almost never see NiMH packs in battery powered RC cars. NiCad's are still used in cars because their extra size and weight over a Lithium pack is actually a net benefit because it keeps the center of gravity low just by making a flat pack as close to the skid plate as possible, a lithium car you might actually have to add weight to get enough traction, since NiCad's are cheaper than lithium cells it's a no brainer to use them in some situations. Cadmium being toxic is a non issue as long as the cells are disposed of properly, you'll see the same warning lable on NiMh and Lithium batteries because even if they aren't as toxic as Cadmium there nothing environmentally friendly about the chemistry used in ANY battery.
Sanyo still makes NiCad's and still markets them, because of the applications they fill they still work great. NiMh's are more for consumer electronics because they tend to power handheld devices where energy density isn't critical, Lithium is taking over much of the mobile device market but NiMh's will probably always be used for some device, the chemistry is cheaper than Lithiums.
They do still use them in those mini RC cars, I'm, not sure why, although peak discharge current might have something to do with it. Those little cars are putting those little batteries under relatively speaking major loads. Try getting 10 or 20C discharge rate out of a NiMH, your voltage will drop through the floor. The current good Lithium chemistries aren't as good discharge wise as NiCad's though you can cheat with Lithium's easier and add packs in parallel to increase max current, but pack management is more critical because 2s2p or more complex packs have to be taken care of properly with an intelligent charger. With a lower voltage hobby NiCad pack it's a straight series pack so easier to manage. Depends on if you need that energy density and weight savings that Lithiums provide. If you don't NiCad's are more practical where NiMh's have their place as well. I don't see any of the chemistry going away anytime soon.
Just to give you some perspective you can still buy "Heavy Duty" batteries, which are Zinc Chloride based and was patented in 1886. The reason they're still used is simple... They DIRT cheap and still work, even if their energy density is horrid.