Whirlpool txs are quite small, with consistent sizes, so it's easy to calculate the anonymity set with a dead simple algorithm.

With Wasabi's huge txs with many different values those simple algorithms aren't computationally feasible because there's so many possible ways the inputs could lead to the outputs. Meanwhile I've seen Samourai fans claims this is a bad thing, because you can't use some external tools to easily figure out the possible input/output anonymity sets.

The Wasabi wallet of course has a good idea of what the anonymity set could be, as it knows what outputs it created. So it can easily calculate a conservative k-anonymity set.