When they usually aren't all that classically attractive themselves.
So stupid. And it makes it seem like they worship attractive people.
Bella ramsey would be an example in which a bunch of chud nerds call her ugly constantly meanwhile they're not exactly lookers themselves.
Redpillers are misogynists full stop so there isn't much to explain in this particular case.
But ideologically amorphous whiny baby complaining about women in media not meeting their idea of aesthetic beauty is a thing, too. Those folks are looking for entertainment and have been taught that being entertained requires main character women to be "hot", looking at them is part of the enjoyment they've come to expect. A lot of this is socially constructed, including beauty standards that change over time. But that's the expectation that is set up. It's highly gendered and binary: objectifying male characters the same way is increasingly common but still much less frequent than for women. Male characters that are not "traditionally attractive" still get main roles and, relatedly, "get the [hot] girl", a very old sexist trope.
The basic summary of this context is that movies were made to suit (and simultaneously create) some fairly toxic male and patriarchal fantasies and they are still full of these tropes. These are also conscious decisions made by writers, producers, and even directors based on both their personal preferences (often male chauvinist) and a perception of increased marketability due to these expectations of what media provides as entertainment. A self-reinforcing spectacle.
So, the "oh no a woman in media not being hot enough" reaction is... a reaction to media that bucks these tropes. That media is trying to appeal to a wider market or has artistic vision that wants to push back on the sexist tropes. The babies that whine about this are literally reactionary, they're upset at developments that mean the loss of the kind of entrainment they have become accustomed to. They also find an online community full of ready-to-use rationalizations for how this is the woke mob's fault and they're trying to ruin everything for the, poor victimized (usually) white male treatl pi Rd. The existence of that community is a much deeper question that I don't have a fast answer for other than it's all about social alienation under capitalism.