> Why should Uber give any guarantees?

First, "guarantee" is the wrong word to take too literally here. Depending on how you want to look at it, there are no guarantees, even with guarantees.

But looked at more loosely, answering that is really Uber's responsibility. Why did they release it? If it is just a PR release, fire-and-forget works fine for that.

If they want to see wider adoption outside of their firm, there are some fairly obvious things they should do to foster that. Sometimes you release just the right thing at just the right time and everyone else does your evangelism and support work for you, but it is much more normal for your next great thing to take a while to build a user base.