Although you should only use addresses once each, many (perhaps even most) people don't. If you have an address which receives three transactions which you have labelled "Payment from Alice", "Refund from Bob", and "Wage from Charlie", then how can Electrum decide which label to apply to the address? Better to leave it blank and let the user decide.

I suppose you could make an argument for automatically applying a transaction label to a change address, since change addresses really shouldn't ever be reused unless the user is doing something really weird, but then again, change addresses should only be used for just that - change. Doesn't really make sense to me to label a change address "Payment from Alice" when it actually just contains funds you already owned which have moved around your wallet.