eBay UK have changed their terms to (a) remove seller fees for most private sellers, but (b) instead of paying-out immediately, payouts are four times a year (or on-demand).
That sounds like they’re trying to keep money in their ecosystem. The hope is, I guess, that by paying sellers in virtual “eBay Pounds” rather than actual money in the first instance they’ll encourage those sellers to become buyers again (either of other listings, or of eBay’s postage and other services). You can cash out anytime you like, but you can never leave.
You see the same technique used e.g. by the National Lottery, who pay out “small” winnings into your online account, knowing that the vast majority of winnings are on the order of only a few times more than the value of a ticket, and so players will be more-likely to “re-invest” if they’re not paid-out directly.
Or maybe I’m just being cynical.