There, now it's YC compatible.
More specifically it will be about scaling the brands they buy and cross-selling when possible. A lot of e-commerce brands/founders hit a ceiling around $1-5M in revenue. At that point, you need more experienced operators to get to $10M or $100M. People who know how to optimize marketing, conversions, fulfillment, and who can move into new channels (eg get on shelves at Target or Costco). A lot of online store founders don't want to deal with that.
Once they hit a certain number of brands under their umbrella, there will be cross-selling/marketing opportunities (assuming they're not just buying Amazon FBA drop ship brands). They can combine email lists and will eventually have good data to power product recommendations.
I'm guessing here, but the long-term play is eventually put all brands under a single online store–in other words, a new amazon.
Why not? YC backs a lot of things that don't necessarily look like a classic "software company".
Edit: nevermind, I see now that they are in fact YC-backed. Don't think I've ever seen YC back another "fund"