It's very difficult for these events to refund people. Unless they have some big industry sponsors, a lot is based on ticket sales. Deposits on venues are usually made with the profit left over from last year.
E3 is different because the big companies can choose to eat or write off the loss, or give money more starting capital to organizers for next year. For smaller events like say, a dance weekend or puppet festival, a lot of those are labour of love type events that have been built up slowly over the years. Those will be the groups hardest hit.
Most US domestic airlines are just providing travel credit with no cancellation or change fees. I had to cancel a month of business travel just now on several airlines and incurred no cost—I just have to use the credit in the next year which in my case is absolutely not an issue.