Disappointing? MK 9 was the best selling MK until MKX came along, now MK11 is selling at a faster rate than MKX did. The games are hugely successful, it has consistently sold better than any other fighting series this generation. MKX sold over 10 million copies btw, no other fighting game series comes close. Tekken 7 took a couple of years to hit 4 million, MK 11 did it in a couple of months, again no other fighting series touches MK in sales, MK11 was also the 5th best selling game of 2019 in North America only beaten by COD, NBA 2K, Madden and Borderlands.
WB made back all of the $33 million they spent buying Midway's assets just from the first couple of months of MK9 sales . MK has been a gold mine for WB games so I don't know where you think it's disappointing.