You need much more components for analogue sound generation than you need when you do it digitally.
This means that the PCB needs to be bigger, which makes them more expensive. You can also place them closer together, but the denser the board, the more likely you get assembly errors.
The time a pick-and-place machine needs to assemble a single board depends on the number of components that have to go on there. With less components, you can assemble more boards in the same amount of time which makes it cheaper to assemble them.
Additionally, with more components, the likelihood of a placement mistake or faulty solder joint goes up. This means that more assembled boards need to be taken out and thrown away, which also makes the price go up.
Finally, an analogue board is harder to test after assembly, which takes more time, which is again more expensive.