Pretty much all the real "nasties" in consumer products went away a long time ago, with the exception of stuff that's specifically sold as that.
As an example, lead is a recognized carcinogen and also can be toxic in and of itself. One of the biggest places you'd find it in consumer products was in solder on the circuit boards. Lead free solder has been the norm(and legally required in some places) for quite a few years now-in fact sometimes in detriment to the longevity of the product(I don't do a lot of board-level work, but if I do you'd better believe I'm using lead solder). Carcinogens have been eliminated as much as possible at the manufacturing level, but you can't avoid the fact that things like some plastic pre-cursors are nasty. As an example, ALL PVC("vinyl") plastics are, by definition, made by the polymerization of the compound vinyl chloride. Vinyl Chloride is something really, really nasty and is a known and recognized Class 1(known to cause cancer) carcinogen. It's HIGHLY unlikely that there is still any remaining by the time it reaches you as a finished PVC product, but it's likely going to have a Prop 65 warning on it. ABS plastic is made from styrene, a Class 1 carcinogen(known to cause cancer) and acrylonitrile(Class 2B, may cause cancer). Again, it's highly unlikely that any is still present in the finished product, but you still slap a Prop. 65 warning on it.
Prop 65 is written in such a way that if an article contains a substance, after regular lifetime exposure at the level in the product, may cause a 1 in 100,000 risk of cancer, it must carry a Prop. 65 warning. There are currently 910 chemicals listed on the Prop. 65 "naughty list". The list is also updated every year.
Because that's such a low threshold to meet, and there's enough common stuff that may have touched a product somewhere along the way, it's a whole, whole lot cheaper and easier to stick a Prop. 65 warning than face the risk of an expensive lawsuit down the line. That's especially true given that a product may be in production for a couple of years and you have no idea what might get added to the list in coming years even if it's not currently listed.