Nobody got anything wrong except maybe you? The airport wanted to use corona as a tool to have all airlines unwilling to move evicted from Tegel by government ordered disease closure and not let them back afterwards until BER opens. In between all traffic would have to be moved to old East German Schönefeld main airport. With corona ending now and summer holiday high season coming up right away they did not have the capacity at SXF alone to serve all Berlin traffic. This is why TXL now has to remain open until late October or early November when BER is finally said to be operational.