No business is telling you what you can or cannot do. However, if you want that business to repair a hose for you, then that business has every right to decide whether or not they want to join you in doing it.
There are arguments to be made on both sides here, but if you think "liability" is just an excuse we make up to sell you a more expensive product, then you've probably never had to buy liability insurance for a business like hydraulic hose repair.
Our general manager here at DHH happens to be a volunteer fire marshall. He's a little more safety conscious than most, and he is my "go to" guy on quy on issues like this. If a customer insists on doing something we feel is unsafe, believe me, we do NOT worry about losing that business.