Why don't major research institutions systematically publish their subscription fees to scientific journals?
Presumably an important reason is that publishers contractually forbid libraries from disclosing this information, see for example http://access.okfn.org/2014/04/24/the-cost-of-academic-publishing/:


  And then libraries are not allowed to tell anyone what these costs are. Libraries are placed under huge amounts of pressure not to release this data, and in the case of Elsevier, they are explicitly forbidden to by non-disclosure agreements in the contracts they have to sign.


This is a reference from 2014, so perhaps meanwhile things have changed (but I would guess not).