Explain it then.
The fee is fixed. If the player wants to join you, THAT is what you pay. Why pay more? For a headline?
Unless you're really not sure whether the player will still want to join you next summer. If that's the case, you shouldn't buy him at all. Or isn't that something that Klopp has insisted on?
The football world is a very variable landscape - it changes daily, let alone what will happen in ten months time.
If he has a great season again, the likes of Bayern would be sniffing around because of his €55m release clause and we might be out of the picture. You say "they'd be stuck with a player who'd rather join another side", but there won't be anyone interested in him or tapping him up since everyone now knows he's moving to Liverpool on July 1st. He's happy to join us now and he'll be happy to join us next Summer since there won't be any bids, interested clubs or transfer sagas anymore. It's basically a "buy and loan back" deal for us to lure Leipzig in doing business with us.
Liverpool: happy, they get the player Klopp wanted from the beginning even if it's only from next season onwards (long term planning, whenever Coutinho might leave). We also don't have to pay his release clause in full next year but can probably pay the fee in installments, which basically makes the extra €10m peanuts if so (don't know much about this financial side of meeting release clauses or paying in installments tbh but others have mentioned it). FSG keeps the fans happy, the perception of our transfer window is that it's been okay instead of a disaster, win win.
Keita: happy he got his move even if it's delayed by one season. He knows he'll still be at a big club with a phenomenal upgrade in wages even if he has a poor season or gets injured.
Leipzig: wanted to keep the player for one more season and they did that with this agreement. If he has a great one, they'd lose him next Summer for less money than they do now, his €55m release clause. If he has a disastrous season, they still get to shift their player for a very high fee.
I don't see how there are any losers in this deal. The medical had to be done apparently because it's obliged if players switch clubs or something like that, otherwise it would look daft indeed. I guess it's just general fitness, conditions, heart checkings amongst other basic things cos you can't account for future injuries of course.
If you want to call it insurance, fair enough. At least we
have that insurance now that he'll be ours next season, something I'd highly doubt if this deal hadn't taken place this transfer window.