Yep. It's Uber that's to blame.

Public transit ridership in major US cities has been flat or declining over the past few years. Several authors have attempted both to explain this trend and to offer policy recommendations for how to respond to it. Past writing on the topic is dominated by theoretical arguments that identify possible explanations, with the few empirical analyses excluding the most recent data, from 2015-2018, where the decline is steepest. This research conducts a longitudinal analysis of  the determinants of public transit ridership in major North American cities for the period 2002-2018, segmenting the analysis by mode to capture differing effects on rail versus bus. Our research finds that standard factors, such changes in service levels, gas price and auto ownership, while important, are insufficient to explain the recent ridership declines. We find that the introduction of bike share in a city is associated with increased light and heavy rail1 ridership, but a 1.8% decrease in bus ridership. Our results also suggest that for each year after Transportation Network Companies (TNCs) enter a market, heavy rail ridership can be expected to decrease by 1.3% and bus ridership can be expected to decrease by 1.7%. This TNC effect builds with each passing year and may be an important driver of recent ridership declines.  

But it's not JUST Uber/Lyft. It's the failure of transit agencies to respond TO the competitive pressures provided by Uber/Lyft. Providing 'circulation' on transit has largely been a myth (Chamber of Commerce dreams of shuttles and loops and circulators are just that). For 95% of people, it's not worth the wait to save the walk).

The idea that it's good for your bus to stop every block is stupid. Every stop costs time, and choice riders choose on time (and reliability). More stops also impair reliability: With so many stops, each stop has (on average) fewer people. But there is no way to predict which stops will have passengers to pick up and drop off at what times. 

To be successful, public transit agencies need to focus on what mass transit can do, that Uber/Lyft cannot: moving a lot of people very quickly. Focusing more on mobility, and less on access.

And how to identify WHERE to cut such services? Easy--just check the map of where the Uber pick-ups are.

source

Where the Uber pickups are, someone has gone wrong in transit provision: Maybe too much is being provided, maybe too little. Maybe it's at the wrong hours, maybe it's going the wrong place. (Uber is expensive, and people don't use it for kicks).