How much would these train + Lyft tickets cost? If you charge a flat rate you risk the someone paying $5 for a $25 commute. What if a taco bell executive gets kicked off the Lyft platform for abusing a driver then buys a trainLyft ticket?
If you charge a flat rate you risk the someone paying $5 for a $25 commute.
Then you make a loss on that ride. Making a $20 loss occasionally is fine if you're making $1.50 profit on the next 500,000 rides, especially if you'd only get 5,000 rides without the flat fee. This is why you model your market structure properly and use as much data as you can lay your hands on to find a workable price point.
It's trivially easy to dream up reasons why, completely hypothetically without any research at all, something might not work. It's not very helpful though.
For what it's worth, where a friend of mine lives in a city in the North West of the UK, getting an Uber is cheaper than taking the bus.