There are a lot of interesting problems in vehicle routing, route optimisation and GPS data processing. There often aren't good libraries which solve them with enough flexibility and performance, and better algorithms are being researched and published all the time. Thus it's quite common for companies to develop in house solutions. A blog post by food delivery comoany Ocado [0] was posted on HN a while back, and I'm sure companies like CityMapper and Strava that work with maps (as well as Google and Bing of course) are constantly trying to improve their algorithms.
[0] https://ocadotechnology.com/blog/ocado-internet-of-vans/