Why is this not implemented inside EEVEE yet?
you mean natively? it looks like you’ve linked to a node group that does exactly that in eevee.
as to why its not native yet, probably it just hasn’t been prioritized, potentially because it can be accomplished through existing node setups.
looks like there is a feature request for it that you can vote for: https://blender.community/c/rightclickselect/93cbbc/
i know for me, getting eevee vertex displacement from within the shader would actually be my preference, since it is more limiting to use the displacement modifier which still uses blender’s old texturing system.