BlaBlaCar does have a product in market for shorter trips, it's called BlaBlaLines: https://www.blablalines.com/ - although it's unclear what the adoption has been since they launched last year in 2017 in France.
The challenge with shorter-distance, shared commutes is finding people who are leaving and arriving at the same location. This is because people are not very flexible when it comes to heading and coming back from work: they need to get there on time, without any detours or delays.
This means that typically, you'd need to get people working at the same company or in the same building to create a successful carpooling program. Making it work outside of the scope of a regular schedule is very difficult.
This is why companies like Uber and Lyft pay drivers to show up on demand, as in this model, you have more control over the supply-side of the marketplace, providing a more predictable experience for passengers.
It'll be interesting to see how this goes, as Waze has a very strong community of drivers. It's a challenge though, as some mentioned in this post, in that there is decent overhead in managing drivers, passengers, conflicts and everything that comes with building an online marketplace with a community angle.
Disclaimer: I'm the CEO and Co-founder of https://www.poparide.com, a long-distance carpooling platform of 75,000 members based in Vancouver, BC (Canada) and our model is similar to BlaBlaCar's, we aim to fill empty seats in cars on intercity trips in Canada.