couldn't you just water cool the cores and use ramsinks?
Not always. I got a GPU only block and VRM heatsink for a total of $50. And can use it on any GPU I upgrade to. Full cover blocks can only be used with a specific card and are hard to sell off when the card is older than a year or two.It a little more complicated than just cooling the memory chips as the card's voltage regulator circuitry also gets pretty hot and need cooling. When you buy an aftermarket cooler you do just add a few ram heatsinks and some type of a heatsink for the VR circuits. But the aftermarket cooler has one or more fans that provide air flow for cooling those additional smaller heatsinks. So unless you want to watercool and use fans it best to buy a block that cools everything.
But were not talking about all cards. Newer enthusiast cards generate alot more power circuitry heat than there older counterparts. And why spend $500 on a card and then spend extra to improve the gpu temps but downgrade the power circuitry cooling.