Is an NP-hardness proof of an NP-hard problem considered a contribution? I am solving a problem that is claimed to be NP-hard elsewhere, say in the paper [XYZ]. The NP-hardness provided in [XYZ] is complicated and uses advanced techniques. After some research and work, I succeeded to give a simple and clear proof of the NP-hardness. I am wondering if this is considered as a contribution or not? I am trying to motivate my work but I didn't find a similar path.

I don't know if this is the right place to ask or should I go to academia?
There are venues that are interested by elegant proofs of existing results, see for instance the Symposium on Simplicity in Algorithms.

So yes, in some cases an elegant proof can be considered as a contribution, especially if it offers new insights.