[1] https://www.tshaonline.org/handbook/entries/bush-dome-reserv...
Basically political bike shedding so elected officials could avoid making any hard or controversial decisions that would have a material impact but maybe upset some folks due to raising taxes or reducing spending.
A strategic petroleum reserve makes a lot of sense, petroleum is part of the food supply chain and it'd be stupid to be in a position where a short disruption could cause people to starve. Not to mention the military implications if an army can't zoom around because the petrol stations run dry for whatever reason.
I don't see anything on the list of uses for helium that looks particularly time- and helium- sensitive in the way that a strategic stockpile would help with.
I'm not seeing any need for a strategic reserve here. There aren't any strategic issues. It is a bit far-fetched that a helium shock will even lead to the end of MRIs.
Also, last I knew about it, the reserves were only reduced, and the US still has some. I have absolutely no idea on the cost/benefit of it, but I don't think any other country keeps a large reserve of Helium.