The thing with looting is, when you are hitting a corp from an ingame POV you want to be as fast and efficient as possible, not spend two minutes each corpse to strip it of valuables and afterwards haul around more weapons than you could ever possibly use during the run. In contrast to most fantasy RPGs, you don't constantly travel and carry all your possessions in a backpack, but reside in the same area for long stretches of time and only carry stuff you'll think will be useful in the near future (that is, everyday life or the next run). Of course you can also come across situations where looting everything that isn't nailed down wouldn't be viable in other RPGs, but in Shadowrun those situations are the norm.