They have to have the no-show penalty otherwise people would hoard. Disney has trained us to book everything (like ADRs) “just in case” so they need to have these rules. Same with the $15 no-show rule for ADRs.
I agree in concept that same-day cancellations should go into the pool for same-day reservations. But also, not every MK holder lives close enough to respond to a same-day reservation. When would the cut-off time be for same-day cancellations? It would be difficult to work that logistically and would really only benefit people who live very close to DLR. If there were no penalty, reservation availability at all times other than same-day would be much, much worse than it is now.
It would suck if you live 3 hours away and always have a really tough time getting reservations because locals are hoarding and cancelling at noon to let another local grab the spot.
Now, I hate the reservation system in general. I think they should just do a cheaper version where your entry is capped (maybe 3 days per month?) and then a more expensive version that’s unlimited with no reservations. But if they’re going to have the reservation system, there has to be a no-show penalty otherwise you’ll have tons of no-shows.
There are gyms/workout classes where you pay a subscription for unlimited passes, but if you no-show, they charge you extra for not showing up! That’s to prevent the same thing.