Why preamp "helps?"

Gain is not the only factor in play.  The preamp / volume control source output impedance is a big deal, also, particularly with low input impedance amplifiers and long cables.  In these cases, an active preamp with low output impedance provides a better match to the load presented by the amplifier.  

So the real answer of passive or active depends on what you are using it with, particularly on the load side.  Tube amps tend to have high input impedance, so a passive preamp can work well.  Many solid state amps have lower input impedance, and for FET-based driver stages, high input capacitance.  For these loads active preamps work better.  As in all these considerations, use your ears to make the best decision on which way to go, for YOUR system !

Gents, I have built and used a PassDIY B-1.  It is excellent, and it doesn't use any IC's, just a discrete, JFET-based buffer and some good quality film caps.  I built it with a pair of ALPS RK40 pots (Black Beauties) for about $200 and a couple hours of soldering.  If you don't need gain, it provides the most flexible and cost-effective volume control you can buy.  But it IS active because of the buffer which neatly solves the impedance issues.

I think some of us are getting caught up in semantics.....a passive preamp has no impedance matching without transformers (Jensen and Luhndahl make the best).  An active buffer may be better for wide bandwidth.  Cost-effective circuits are readily available.  If you need some gain (even as little as 10 dB), you definitely need to go active.  There are many options for those too.  

You need to turn off your mind and use your ears to find the best one for your system !