I didn't want to imply they are dropping all the time. Should probably have said "occasionally" rather than "frequently". I guess my number of dispatched Condas is a lot closer to 700 than to 7. If I were to hazard a guess, I'd say that about every 15th drops PIs. It may well be linked to factions ot states as well, which I do not pay attention to.
I currently fly missions out of Codorain, to finally rank up with the empire and get a Cutter. Delivery missions usually send 4 Condas against me. As I usually stack them, and get randomly interdicted as well, I'd say I meet about 10 Condas per sortie. Pirate assassination missions often send me against Corvettes. Shot one down last night, in one of Codorain's neighbour systems, and it dropped 1 lot of PIs.
It still takes very long to collect them, and if you fly out looking for them as you need them for an immediate engineering project, it can certainly be a frustrating experience.
I cannot rule out that the drop algorithm is flawed. But if I were to hazard a guess, I'd say PI drops are linked to a series of conditions, and if they are met, there is a certain chance they will drop. But that's just me guessing. All I can say is that I have plenty of PIs. I'm not implying that those who don't do anything wrong.
But there are other mats that I never find - military alloys for example, or imperial shielding. Even some low grade mats, like mechanical equipment. Simply because these mats are hardly ever dropped by the ships I'm usually fighting, and I cannot be bothered to go after the ships that drop them.
Most of the time, I will scoop up whatever my enemies drop after I'm done with them. And as soon as first mats get near their storage maximum, I will visit the nearest material trader and trade all material stocks over 50% for mats that I hardly ever find.
I also always select mission rewards that involve mats or data. Credits is the one commodity that you can always earn easily, if needed. But mats and data, you can never have enough of.
Finally, on a lighter note:
That qualifies as a newbie to me. CMDR since 1986.

Back in those days, we went 20MM barefoot through a snowstorm on an ice planet to collect our mats. Kids these days...