People do this a lot. This is a well-known and old issue known as "Hidden City Ticketing" and goes by other names, as well. It is against the typical Contract of Carriage agreement passengers have their airlines, though it's hard to actually enforce: https://travel.stackexchange.com/questions/17984/is-leaving-...

Note that while this tactic can be money-saving and useful in practice, it does have certain downsides, like if you need to check luggage, or if you expect to collect your airline miles and segments (typically requires completing the full itinerary, though not always).