Here's another way to look at it: Facebook, Google & Twitter sell their software to advertisers that allows them to reach their target audience. Here "selling" is actually a service.

Uber is mostly a software company - the cars are owned by the drivers. When you pay for a Uber ride, you're infact paying a part of it to the software which helped you find the ride.

Apart from that, there are huge swaths of enterprise software companies in every industry/domain you will probably have never heard of. Some of them are even billion dollar companies.