There's a legitimate reason for that. Tom Scott did a video on it.[0] It basically boils down to telephone switches starting to compress the audio. Compress and decompress multiple times (by various companies) on the way to you, and the quality degrades very quick.
There are billions of calls made using a phone number still.
"Across the world, we make 13.5 billion phone calls every day, using mobile phones. The average person makes or receives around eight phone calls every day, meaning that the US deals with around 2.4 billion phone calls across the 300 million cell phone users" that's from 2023 source.
Here's a 2019 one about US:
On average, people make and receive a total of 178 calls per month
Of those 178 total calls, 93 are calls received and 85 are calls made
Not just older people either:
"80% of Millennials and 84% of Gen Z-ers use their phones during 2020 for phone calls".
And somehow, on analogue circuit switch phone call mode, still sounded better with less artifacts than most mobile phone calls!