unanswerable question without more data. But as many have mentioned, there are many solid reasons to use capacitors. If we simply accept you assertion that some preamps have a relatively large complement, the quick answer would be "because they need to isolate lots of inputs and outputs". But that's pure speculation.
Why in fact do so many recipes include a lot of garlic? Maybe we ought either ban garlic or add it to cakes!
I'll also note that ot all capacitors you see are actually directly in the signal path, and that there are many engineering solutions to the non-linearity of common electrolytic capacitors. While the purist in me wants to eliminate them, more often i find that they free me to make bigger improvements and its often worth the "cost"