Years ago I worked in customer service. There was this guy who came in to to motivate us. He talked about the work of someone named Bob Farrell who had a chain of ice cream shops and sold burgers. He had received a letter from a disappointed customer. The customer had been given the extra pickles on his burgers for years and now one of Bob's employees told him he now had to pay extra for it. The customer said he'd never come back. Bob could have said "what an entitled idiot" and kept charging for pickles but he took that letter as a calling for how you should treat customers - just give 'em the pickle. It costs you next to nothing to give the customer the pickle and it makes them happy.
Minio doesn't have to give non-paying users anything, but the story still applies. Give them the pickle. It costs nothing in the grand scheme of things, and if it does, ask for donations like any open source project would do to cover your costs. But as others have pointed out, Minio is not an open source company, they are a commercial company that has source available.