The gallium in liquid metal is parasitic. Basically over time it'll eat away at the metal surface it's on, and replace those molecules with a gallium alloy made up of the gallium and the surface. With liquid metal, it'll need redoing every 1-2 years as the liquid slowly sinks into the substrate. After 5-6 years ±, there's enough alloy that that process basically comes to a halt, you'll be moving onto a different platform by the time you even get close to redoing the liquid metal again.
The better standard pastes generally last 8 years ±, before the ethers and 'paste' part of the paste break down chemically enough that the silicates doing the actual thermal work become unreliable.
A well applied paste job, with good paste generally outlasts the time most ppl own that particular pc.
Liquid metals have a Thermal advantage over any paste, not in ability, but in speed. Metals transfer heat faster than silicates do. So it makes sense to use liquid metal Under the IHS vs Tim, where it doesn't need reapplication every other year since it only has a single surface to parasite from, so dimensions don't change. And that's assuming the cpu uses Tim and not solder.
Once that heat hits the IHS, it's out of the cores, and therefore immaterial to the cpu, so pastes work just fine and are more reliable, easier to use, safer all around, even if they give up a degree or five in temps.