No Brain: No Pain?

Vegans feel that eating multicellular animals or their direct products (like honey or almonds) is wrong. They generally want to avoid animal pain in their dietary choices. A small minority of vegans, however, have recently decided that oysters and mussels can be consumed. They judge that these seafood items, "feel no pain". This seems, however, a tad inconsistent with strict veganism? (https://www.theguardian.com/environment/2024/sep/12/ill-have-them-with-hot-sauce-should-vegans-eat-oysters). Such folk, class themselves as followers of 'bivalve veganism'. Bivalves are certainly animals. They are, however, sessile. They don't move about much, remaining in their protective shells. This means they don't writhe about, when faced with potentially 'painful' stimuli. That doesn't, of course, mean they are incapable of feeling pain. Oysters, for example, produce pearls, in response to internal 'irritants' like grit. It's true that oysters and mussels don't have much of a 'brain'. Their neural ganglia are, however, not too different in size from those of an insect or a worm. Insects and worms are, of course, much more likely to wriggle or try to escape. Is that the reason, they are not also on the 'menu'? Oysters and mussels are also in the same Phylum as the squid and the octopus. Squids and octopuses are the biggest-brained invertebrates. Isn't eating an oyster less 'vegan' than eating honey?