They missed the first round of crypto around 2013-2014 because Bitcoin was too controversial for these well established big IT companies and they were simply afraid to participate or they just missed it. So they are few years behind and now many of them are building some blockchain-related services. On the other hand setting up crypto farms and mine on them is something quite different and I guess too risky with uncertain revenue so they stick to their traditional business. Much more I would expect big banks building buying super-computers and building crypto farms (on the other hand it's probably much more simple for them just to buy crypto directly - coins are still very cheap in relations to their budgets).