well it's definitely easier to sustain for a longer period of time, for sure. you can be a shytty e-tailer and exist for a few years selling your wares at half off over and over again; I've seen many high and low-tier sites come and go after a big splash, too many to count.
karmaloop's problem is/was, and I haven't been to the site in years because why the fukk would I go there, it had no position in the market. No unique shyt. No reason to exist. The only thing it had going was regularly discounting and selling shyt to me for under msrp (n&f jeans years ago, before plndr), which isn't exactly a good business model long-term. shyt half the brands they invested in are expansion-minded thus can be gotten at fukkin hot topic and etc now. Also, as others have pointed out, nobody cares about random streetwear labels anymore.
And here we are. similarly, I look at sites like ikkon and wonder how they're still afloat. Year after year, season after season, everything is 50-70% off.