I haven't played in a very long time and I go to train my magic and I realize that spelly no longer require chaos/death/blood runes. What are they good for now? Why still expensive?

Death and blood rune requirements were removed from the standard spellbook with the advent of Evolution of Combat, but they are still needed for burst and barrage spells when using the ancient spellbook. This is popular, in particular for the blood spells, since they are AoE and provide secondary effects such as healing, enabling some of the fastest sustainable magic experience in the game without even using food (i.e abyss and other places). Even regular elemental runes have risen substantially in price though. They were pennies for quite a while.

 

I'm not sure about the price of chaos runes though. There are three spells in all of RuneScape that use them - Curse, Vulnerability, and Teleblock. I suppose it's a relatively low demand, and relatively low supply (they are a pain to craft) and the price reaches some sort of equilbrium.