It is true that VOIP is high definition audio with an upper range of 7khz or higher. Copper voice frequency is as stated above limited to usually 3.3khz. The use of fiber to the residence can improve that, but not everyone is on fiber.
Copper landline is also prone to bad connections cause by corrosion or lose hardware. The old 500 series phones had to have the mouthpiece removed and rapped on a hard surface to fix ‘compaction’ where the carbon in the mike would give problems) A digital voice signal can be retransmitted automatically if packets are dropped. There si a reason the phone company (Bell at the time) started convering local offices to ESS (Electronic Switching Systems).
As more and more people switch to satellite and cable-supplied internet, the need for hardwire to houses for telephones will be deminished considerably. Even alarm companys have transitioned away from hardwired connections to cell-phone connections. It is easy to disconnect or circumvent hardwired loops for alarms (trust me :-).
In the past the telephone company owned all the plant from the telephoen you used to the copper wires to the central office to the local and then long distance carrier. That dramatically changed when you could choose to buy your own phone, use a different long distance carrier (the early ones were MCI and Sprint) and then could drop hardwired lines completely. Think about all the hardware between your phone and someone overseas. Now think how much of that is eliminated when your call bypasses TPC (The Phone COmpany) and goes through a cable aloing with TV and Internet and perhaps through a company in Canada that supplies your long distance and local calls. Almost all of the traditional phone service completely bypassed. That is the main reason you don’t see payphones anymore. Who needs that when we have cellphones we can use as we go through TSA stations instead of missing a flight because the airport pay phone is fixed in location?
For some the hardwired connection works great but the cost of keeping that system running will just keep getting expensive. We have a building near me where all hardwired connections route through. My calls never touch that building. I can’t imagine what it costs the local phone company to rent the land and supply service to others. It explains the $20 and up monthly costs compared to my 80 cent a month cost. Hardwired phonnes ara dinosaur.