If blocking the bot prevented their interaction with users and the posts/comments those users make that would be a good solution, but as is blocking is just an "eww I don't like this, I don't want to see it" instead of "This entity will not be able to interract with my account/posts". In this case there is concern regarding the bot's behavior, and the unwanted exposure it gives to users who may not want it, which blocking doesn't solve because it doesn't provide an opt-out from replies, just to stop seeing the replies.