Cryptography has a peculiar approach to the threat of quantum computers, because it is not acceptable for some of the data and connections encrypted today to become decryptable even thirty, fifty years in the future. That means that the question is not "are QC coming soon" but "might QC plausibly come into existence in the next half century". Since the answer, despite not having a precise consensus, is not "no", here we are.
This is also why you are seeing a lot more progress on PQ key exchanges, as opposed to signatures: signature verification today is not affected by QC fifty years from now, while encryption is.
There is also the problem of embedded devices. Some of these will still be operational in 20 years, at which point a "cryptographically relevant quantum computer" might exist. So we want to ensure today that these devices can support post-quantum algorithms, and depending on the device, this support might need side-channel and fault protection.
In some cases we can add support with a device firmware update, but things like secure boot flows and hardware accelerators can't always be updated in the field. And we need to make sure that the devices are fast enough, have big enough key storage, RAM and packet sizes, etc to support the new algorithms.
It's also important to have an established history of use and vetting so by the time PQ is needed, systems with a long history of security are available
This is also why you are seeing a lot more progress on PQ key exchanges, as opposed to signatures: signature verification today is not affected by QC fifty years from now, while encryption is.