If enough of us report it
('Issues: Other' https://www.kaggle.com/contact#/other/issue )
they might do something about it.
There's not really much connection between asking someone to redo their whole website and them actually doing it. That seems like work.
Also, the discussion forums aren't "their whole website". Kaggle is about running data-science notebooks and kernels, on GPU/TPU(/CPU), and noone's suggesting they change that. The discussion forum (or competition leaderboards, or datasets, or submission API) are adjacent pieces to that.
There absolutely is, in this case. Kaggle was acquired by Google in 2017, and is a showcase for compute on Google cloud, Google Colab, Kaggle Kernels. Fixing the JS on their forums would be a rounding error in their budget.
(Also, FYI, I've previously posted feedback pieces in Kaggle forums that got a very warm direct response from the executives, although that was before the acquisition.)
So, for the average website, you'd be right, but not for Google Cloud/Colab's showcase property.