Because NPCs don't use properly engineered shield boosters, so we live in this whole other game rules where a player stacks 10k mj of shields and solo brute forces through even the hardest pve content like wing threat level 6-7 stuff that still isn't at outfitting that rivals players. Heck, we get the ocasional thread that NPCs shouldn't even use chaffs.I really don't get why this has turned into another PvE vs PvP crowds argument (mostly from just one side). I actually reject the idea that such a strict separation exists and that they are opposing groups.
It's a simple matter of game balance.
If NPCs used shields like players do, within hours there would be consensus on the state of shield booster stacking.