That wave thing or that tipping the ice over thing are both behaviors they have to learn as kids, like all of their many hunting methods. If that specific orca population doesn't usually hunt seals resting on ice, they won't know how to do it. Adult orcas have a really hard time adapting to a new feeding strategy. They may figure something out eventually, but that's not something they pull off in a couple of minutes, it takes so long they're at serious risk of starvation when their normal food source disappears. Maybe neuroplasticity plays a role here, just as humans learn new languages much easier when they're kids.