True, but it is not only the data. Even if it was why aren't the big 3 doing this already? Tesla is a technology company more-so than a car company. They employ the engineers focusing on machine learning and gathering the right data to support that. This would be a brand new area for Ford, Chevy, etc... I'm guessing. Not that they couldn't ramp up, but I don't think it would be as easy as you seem to suggest.
Walmart had the funds to overcome and mimic what Amazon was doing early on as well and they didn't. Why not? Some companies are set in their ways and have trouble seeing the future...or at least be willing to sacrifice short term revenue goals for long term gain (often times big profitable companies act this way).
TBH, I own a Tesla. I agree they are likely not the leader in the best technology for driverless cars, they are definitely the leader in affordable driverless cars. The interesting thing is autopilot gets better and better on streets you drive over and over again. Tesla's have ruined my experience for driving any other car. I'm sure someone else will make some great electric cars in the future as well, but right now there is nothing that compares to it overall.
Edit: To add one other point on my initial paragraph (and coincides with my last). Tesla not only gathers the data but has the autopilot features to be able to test changes to the algorithms in place and improve them over time. Even if the big 3 started collecting this data they are far behind in the ability to even simulate much less enable it for real feedback on the roads.