It's not surprising.

Etihad owns topbonus. Better to allow customers to redeem for flights on your own products -which apparently is restricted only to economy redemptions, i.e. no upgrades, no biz class - than to go around trying to obtain new flight partners for a dying programme. There's no way topbonus miles will ever be redeemable on oneworld again, and it is hard to see the current owners persuading any new airlines to sign up as partners, given that it is the FFP without an airline.

It is good of them to give any customers having a topbonus balance the chance to use them up on something half decent - I can't see the programme lasting much longer. This just seems like part of an orderly wind-down - so kudos to them for allowing people to spend the miles, rather than just disappearing and taking the balances with them.

(Whether every topbonus member wants to redeem for EY-metal flights is another thing).