There are valid edge cases where you want traffic to be encrypted on the internet, but be readable by some intercepting device under your control. Parental control software has done that for decades, and there are (in my opinion misguided) regulations in some sensitive industries that suggest having to store a decrypted traffic log.

Corporate MitM boxes are quite prevalent (they caused 5-10% of TLS 1.3 traffic to get dropped before they changed the protocol to fake TLS 1.2 session resumption) and when it comes to corporate-owned devices, that usually shouldn't pose too much of a privacy/security issue.

These setups were a lot easier back in the day when TLS let you set static keys, but you can still dump TLS key files and/or reject all non-proxied traffic with your MitM proxy if you want to do such a setup. It'll break loads of apps thanks to certificate pinning, but that's probably a good thing for such corporate networks.