The aluminium was in contact with the water, that's the issue. Absolute stink kicked up about their entire 3000 series Waterforce cards dissolving, and nobody trusted them again.
Also pre-blocked cards don't have much resale value. You may lose money on the waterblock should you come to sell, but the majority investment is on the GPU, so slap the air cooler back on and you're good. So personally I'd go aftermarket GPU block.
Can't remember where I saw it, but somebody's done a teardown of the 5090 FE and replaced the liquid metal with regular TIM and - to the shock of nobody - performance was unaffected. So it's entirely possible that Nvidia put liquid metal on their FE as part of its insane overengineering, and AIBs went "oh OK, we can do the same and charge extra because it's premium", not because the cooling solution requires it.