It's possible that Google or Uber could make an official announcement explaining the feature removal, but for now, you'll have to use the Uber app directly if you want to book a ride through that service.
The exact reason behind this is unknown, as Google hasn't said anything besides "you can no longer book Uber rides directly in Google Maps" on a support page. We'll take that over no cab-related information at all.
Google made a big fuss about having the ability to book an Uber through the Maps app when the functionality was added in January 2017. If you decided that taking an Uber was what you wanted, you could book the ride right in Google Maps (assuming you set up the integration with your Uber account previously).
Uber has certainly changed how people get around. This meant that while searching for location of places, users would also be able to hail an Uber within Google Maps itself. You can still look up the route in Maps and then "request the ride from the Uber app", Google suggests, but it has removed direct Uber booking without providing a reason.
It's unclear as to why the integration was scrapped, considering that it was a win-win for both companies. If you don't have the app installed, you will be sent to the Google Play Store where you can install it.
Interestingly, when we checked the Google Maps app on an Android device, the Uber option was not present at all. If Google was looking to cut ties with Uber, why not go all the way? However, for reasons now unknown, Google just removed that integration. Still, it wasn't a free-for-all: Google worked with specific companies on a country by country basis.