Because if you try the same on a big analog modular you won't get very far at all - less far than you can get with code, given that very basic singing synthesis was already a solved problem back in the 1960s, and systems like Vocaloid have been commercial products for more than a decade now.
https://www.youtube.com/watch?v=hDsJCJ02184
...Which is the core problem with analog synthesis, whether it's a modular or a box-of-knobs synth: it's the synthesis equivalent of writing code in BASIC.
You can do it, and it's good for certain kinds of jobs.
But even though a wall of knobs and wires looks like the last word in musical openness, it actually puts some very rigid limits on the complexity and sophistication of what you can do. And worse (IMO) it trains you to think inside those limits instead of encouraging you to explore beyond them.