It's possible that Anthropic sees that the loss of $20/mo customers could be offset by the customers purchasing the $100/mo plan
Loss of customers is the wrong direction
They really don't need to subsidize unprofitable customers at this point when there is a line out the door to pay thousands of dollars a month per user, that are revolting because they aren't actually being able to get reliable uptime.
They have all the growth they need for now, they really don't need the cheap users.