I really don't understand how people end up with inventory problems....

I am a person who:
- Plays multiple classes with some shared gear, but also several pieces unique to one class
- Maintains a plethora of materials useful for at least 3 different crafts
- Keeps U/U stuff, beastmen currency, and other stuff that is mostly just for collecting
- Keeps some +3 mats I know will be useful later
- Takes the time to sell things like spare gear in wards
- Has millions upon millions of gil still

All this and I still have:
- One retainer who sits around 90/100 inventory at all times
- Another retainer who sits around 75/100 inventory at all times
- 60/100 inventory on my character (before venturing out of a town)

How in the unholy hells of Darkhold do you friggin fill up your inventory? Do people honestly save every scrap of rat feces that floats their way? VENDOR STUFF.