Worth noting 48KHz audio is now a commonly encountered standard for video. Not to say it’s necessarily audibly discernible from 44K but it’s obviously not quite as straightforward as 44K being the end of the story.
In the early days of digital audio, and before oversampling was possible, the anti aliasing filters were analog circuitry.
It's very difficult to cheaply implement a 20kHz brick wall filter with a 2kHz sideband.
Doing it in 4kHz yielded better results at the cost of slightly faster ADC designs.
I believe this is why 48kHz designs got the foothold in professional audio circles. The analog parts of those designs were WAY better sounding.
Once oversampling became common and affordable, the anti aliasing filters where implemented much more easily in the digital domain.