Indeed my CTA express bus only seems to get more crowded. But I suspect the vast majorities of the ridership losses are off-peak trips.
Here is a plot I just made of Chicago Uber+Lyft usage vs. hour of week based on the public data dump (this is 7 months of data from November 2018 - June 2019). The color axis / text is showing the fraction of rides starting in that hour (so the integral of this plot is 1).
FYI the total number of rideshare trips over these 7 months is 73.2 million.