The principle problem of the Panopticon metaphor is rooted in Bentham's original purpose for the structure: behavioral modification. As Walker puts it, Bentham believed that the mere act of being being watched constantly would alter a person's behavior, adding a layer of accountability and therefore pushing the person in question towards a more moral or sociably acceptable course of action.
As Walker points out, however, modern surveillance is completely incompatible with this idea. He uses the example of digital watchers overstepping their boundaries, but it is apparent that even in everyday, mundane examples of surveillance, people simply don't change their behavior. For example, consider Facebook. It's no secret that Facebook tracks and stores almost every bit of information its users will provide it (how else will Zuckerberg learn what it means to be human). Following the Cambridge Analytica scandal, that knowledge became headline news; everyone knew Facebook was effectively spying on them. Since then, Facebook has gained almost 100 million users.
If people know they're being watched, why do they opt into the system?
Simply put, it's because it's impossible to live without the system. The Panopticon may have been a prison, but technology is so integral to modern life that opting out simply isn't an option. Beyond just Facebook, social media provides a fast and efficient communication system, and Google is the premiere tool to find information in the blink of an eye. These systems are unlike prison in that we want and need to be a part of them to survive the modern world. They've made life easy and convenient enough that the expectation is that we use them to augment our abilities to both work and play. For that reason, the Panopticon is a defunct metaphor that cannot encapsulate the complexity of modern surveillance. It's not just that there are too many actors that watch us from the watchtower, but that we have to remain in the prison if we want to maintain a standard of living that we're used to; we've collectively decided that the opportunity cost of opting out of the system is too great, even if we maintain some semblance of privacy. Yet, we don't begrudgingly use these apps, either. People still love to browse using Google, wish their friends 'happy birthday' on Facebook, and post their latest fire selfie on Instagram.
Altogether, we just really don't care that we're being watched.