So what exactly is the concrete downside here, apart from the icky word "platform", that, in this context, means "a security chip that's not removable", ie as opposed to a Yubikey or such.
Websites will, at their option, be able to require Apple hardware to use them.
Attestation has allowed a website to lock to a specific vendor for 5+ years.
Last I checked, Windows won't let you use self-signed attestation keys for your homemade devices.
perhaps it's a totem, a reminder, that not all tech is interested in working together, that unlike the web itself you are entering an Apple or an Atari or Acorn specific encampment, for some random examples.