Rather than continuing to compete with Didi Chuxing, the dominant ride-hailing service in China, Uber sold its Chinese assets to that firm — essentially ending competition in ride-hailing in that country.
This transaction raised several concerns. One, Didi and Uber jointly controlled the overwhelming majority of ride-hailing service in China. The nearest competitor had just 3.3% market share as of the time of the transaction. The transaction thus created an effective monopoly for Didi — allowing Didi to charge higher prices and fees, to the detriment of both drivers and passengers.
Two, as part of the transaction, Uber received 17.5% ownership of Didi, and Didi in turn held an investment in Lyft. So the Didi-Uber deal made Uber a part owner of its biggest US competitor.