Here's the thing... you hoard loot.
It's difficult not to. To a certain degree, having Local Leader 2 helps, because you can build a set of shops next to your workbenches so you can sell all that stuff as fast as it comes in. Otherwise, going on sales trips to places like Abernathy Farm and Diamond City is a production.
Of course, that means you need to have a use for those caps, which means either 1) being a lot more willing to spend money at the local scrap dealer or 2) saving for the exceptionally expensive unique items. Note that (1) is also helped by Local Leader 2 since you can buy scrap regularly.
If you're into building elaborate settlements, it's worth noting that Abernathy Farm sells wood, and Diamond City sells steel. Shipments are overpriced, but if you're running short of wood to build that classy apartment complex for your settlers, instead of the standard ghetto barracks, it's the one way to get bulk supplies. I didn't run short of either in runs 1 or 2, but in run 3 I seem like I'm constantly running short because I'm making stuff that's actually liveable rather than just functional.
Side note on building: a decent interior pretty much requires mods, if for no other reason than the vanilla parts don't allow interior doorways. Your choices without mods are either a big barracks or lot of little huts.
Another use for that loot is equipping your settlers. This is semi-functional, unlike the "build nice places" thing, since well-armed and armored settlers are a lot more help in an attack than the standard settlers with street clothes and pipe pistols. Settlements that are close to hostile spawns (i.e. The Slog, Finch Farm) particularly benefit.
That said, even though I'm doing this stuff, I still have a crap-ton of loot at Sanctuary Hills, and I still can't bring myself to stop picking up more.