No reason computers should come with that out of the box, in the same way there's no reason they should come with a DVD drive or a vertical mouse or brand-name webcam, but if that's what you need in your life, any of these are <$100 peripherals.
Because you don't need a $2000 audio interface with twenty XLR inputs with individually controlled phantom power and built in EQ, or even a $299 one that podcasters and youtubers like to keep recommending: if you just want control over your audio, get something like a Behringer MONITOR1 for $60 [1], or a slightly nicer Mackie "Big Knob" passive 2x2 for $70 [2] and go "ahh, exactly what I needed".
[1] https://www.behringer.com/product.html?modelCode=P0C9G
[2] https://mackie.com/products/big-knob-series-monitor-controll...