Are there granted patents for car sharing systems? Assuming Uber, as an early entrant has such patents, how could competitors like Lyft and careem have surfaced after Uber?
The specific patent publication US20120330696A1 mentioned in the original version of this question is a publication of an application, not an issued patent. One way to see this is to look at the upper right of the document and see "Pub. No.:" before that number. Also, application publications have numbers that start with a year followed by a yearly sequence number. Issued U.S. patents have a monotonically increasing sequence number from patent 1 to hitting 11,000,000 in May of 2021.
If you look up US20120330696A1 in google patents you will see it went abandoned. Looking in the Global Dossier (linked from the google patents page) it was abandoned 11/13/2013.
To answer the larger question - patents cover what is in their claims, the numbered passages at the end. To infringe a patent, a product or service needs to have all elements or perform all steps in at least one claim. It is usually possible to work around a patent to proved a similar result. Claims are not for results but for specific structures or steps to achieve a result.
The abstract and specification need to back up the claims and are almost always much more expansive than the claims that end up issued.
To the broader question you will need to do a comprehensive search to see what companies have what granted claims.
One doesn't patent the concept "car sharing", one patents a specific thing, which is described by things known as "Claims".
Part of the invention process, and why patents are granted (in the US, at least) "to advance the Arts and Sciences" is to encourage people to come up with other ways of solving the problem "how can people share cars?"
So long as businesses (or individuals) can keep coming up with different ways to solve the problem "how can people share cars?", and those solutions satisfy the things like the "novelty" problem, there will be no end to the number of patents issued for "car sharing".