This is Google’s Titan security key

Supporting Bluetooth may seem a feature to some end users, but seems to be a terrible idea for a device saying it is one of the most secure on the market.

Bluetooth has been problematic in it's implementations, and has had a myriad of security issues, and issues with end users, guaranteeing the connection will last. The NIST CVE list isn't exactly charming. [0]

Issues like CVE-2018-5383 [1], where the encryption key leaked over Bluetooth for most iPhones, Androids and Macs could render the Titan useless.

[0] https://nvd.nist.gov/view/vuln/search-results?query=bluetoot...

[1] https://nvd.nist.gov/vuln/detail/CVE-2018-5383