Ride-sharing suffers from the problem of clustered networks - you can be a global player like Uber and still lose the entire city of SF to a competitor like Lyft, or feel a minnow like Juno tear into your margins in NYC.
Having bike sharing in your pocket helps you build a wider moat around these clustered networks. If I typically take a bikeshare to the subway every morning, and rarely Uber on the weekend, Uber might win 10 low-margin trips from me during the week (bikeshare to and from the subway every day), and through the use of a loyalty program incentivize me to make my 2 high-margin weekend ridesharing trips Uber trips.
So yes, it is an adjacency, and it is lower margin than ridesharing and capital intensive, but this is a difficult market and at this point in the game it might make sense.