I think this investment doesn't come as quite as a surprise because Uber already partnered back with Volvo not too long ago to equip the Volvo XC90's with self driving tech.....but the more the merry I say. This will give Toyota a chance to catch up with everyone else in the self driving space.
I personally don't want to be driving in the future anymore and have to worry about all the hassles that come with owning a car such as car reg, taxes, insurance, car payments, etc....why deal with all that when you can just have a car come pick you up easily..
Uber needs much more investment I believe to compete with Google/waymo who already has an order for 62,000 chrysler pacifica vans a deal worth around $1.6 billion.... Toyota will be supplying Sienna Minivans for the self driving tech Uber will be equipping them with.....I'll definitely be keeping up with the progress of this new deal with an open mind ;)
Sources - https://techcrunch.com/2017/11/20/uber-orders-24000-volvo-xc90s-for-driverless-fleet/,
https://www.theverge.com/2018/5/31/17412908/waymo-chrysler-pacifica-minvan-self-driving-fleet
https://www.uber.com/newsroom/uber-toyota-team-self-driving-cars/