Other networking protocols coming from a telco background, in particular ATM and ISDN, were all circuit switched, and had suitable resource reservation for QoS.

Other networking protocols coming from a telco background, in particular ATM and ISDN, were all circuit switched, and had suitable resource reservation for QoS. Acceptance of telephony degradation was probably driven by cost: VoIP was free and that made a difference, especially for international calls. In my experience, in 2020 the VoIP calls I make are really high quality, even better than 1980s-style ISDN calls, and the main cause of audio quality degradation are people using "hands-free" setups with their laptops.