Why do preamplifiers have so many capacitors?

@jumia-

     Actually: what was supposed to be a link to the following Vacuum Tube Valley site and reprints, wasn’t, on the last reference.

                               You’ll find some good articles, here:

https://web.archive.org/web/20130604042043/http://www.jumpjet.info/Pioneering-Wireless/eMagazines/VTV/vtv.htm

     Be patient, as you're downloading a complete magazine, in pdf form, for each issue.

Watch some of Ron Sutherland videos.

Or, if you want a more formal textbook, 'The Art of Electronics' by Horowitz and Hill is a bible of practical methods. A section  in Chapter 1 talks about capacitors and their different characteristics.

But also note that although materials are a good guide to how a cap will sound, the method of manufacture also makes a big difference. For example, a Relcap teflon film and metal foil cap sounds quite different from a V-cap. To me. YMMV

I think my sanders preamp has 20K of capacitance

 very very accurate and closest to straight wire with gain ve ever heard

unforgiving pre!

but, a good recording is just that, sounds flawless

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"