Honestly, I think cruise lines (or any business) isn't required to give anything more than a 1 for 1 refund in the current situation. Seems they've been more than fair.
But I have read that cruises, in general, are currently selling for about 25% above last year's costs anyway.
We lucked out on a major RV trip we had reservations on this summer, and the company is letting us move the reservation to next year's trip for this year's price. Or we could have opted to take the full refund and book a different trip for next year, at the prevailing price for that trip now.