Why would Apple make a car?

Because, much like their laptops and phones, the people who are buying them aren't "optimizing for reliability", but rather "showing off"

which turns out to be a pretty profitable venture from Apple's point of view

Because in the medium-term future, cars are going to be all about software, and will be for entertainment almost as much as transport.

All the competition has no path to vertical integration.

Premium product, optimized integration, maximized profits, valuation to the stars.