I'm going to give Apple one potential benefit-of-the-doubt point here, despite the fact that I think there's also good reason to suspect they're not above succumbing to the incentives they have to hobble the web vs native.

If they're primarily about tablet and mobile devices now (lots of indicators that's the case), they're going to be concerned about battery life, performance, and other impacts on user experience. If history repeats itself, they're probably concerned about these things at a level of fussiness that other vendors often don't share. They might well not be on board with wasm for related reasons, or they might take longer to conclude it'll be OK, or work out whatever efforts make them feel good about it.

Or they might just lurve their walled garden a lot.