They don’t have enough gain, so they need an active pre to help the signal along.If it goes loud enough for you, you have enough gain, a passive preamp will NOT compress the music if it’s up near full.
Quote from Nelson Pass:
We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.Cheer George
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp.