I don't understand what some of you are doing with your weapon parts. If there had been a 25% reduction from the start I would only have 750 instead of the 1000 that I have. I had to go look to see what they're even used for because I pay no attention to them.
Trading in for faction rep or infusing and upgrading weapons.
The issue is that they used to be in abundance. The old raids dropped guns like candy, so did crucible, trials, strikes, just playing, etc., and noone needed these guns because you already had them or they weren't as good as the ones you had thanks to rerolling, also upgrades didn't take many weapon parts, so people had thousands.
Year two comes, and you can trade them for faction rep. I have thousands, why not, right? So you do that, and your stockpile is gone, and now you (a) don't get as many guns to drop, (b) many guns are better infused than dismantled, which takes a lot of weapon parts and gives you back none, (c) you can't reroll, so it's safer to hold on to guns you used to dismantle until people figure out what works and what doesn't, and (d) we're all starting from scratch, so we need to upgrade everything.
In another month or so, it won't be as bad, but they're definitely the most common bottleneck for me. I'm constantly running out right now. So it's a bit annoying for Bungie to reduce the drop rate with no explanation.