Online stores should totally care about getting a high cart conversion rate. It basically means people aren't just window shopping—they're actually buying stuff. If your conversion rate's high, it usually means your site's easy to use, the checkout doesn't suck, and people trust you enough to spend their money. If folks are adding things to their cart but then bailing, something's probably off—like maybe shipping costs are too high, the site's slow, or the checkout process is just annoying.