It was never intended to be longer than that. As I said, it was a midseason replacement. They have those every year to slot in in case a new show bombs or to try out during hiatuses.
It's been a common practice in the television industry for decades. Look through your DVD collection and you may notice that some of your shows will have a Season 1 & 2 DVD set before seasons 3 and onward are consistantly a single set, or you may notice the first season has fewer discs than subsequent seasons if it stands alone. That's generally because it was a midseason replacement that caught on.
Many well known shows were midseason replacements with shortened first seasons, such as the Simpsons, Quantum Leap, NewsRadio, Buffy, All In the Family, Happy Days, Family Guy, the Wonder Years and Batman.
Honestly, midseason replacements are quite often where you see the cult hits show up. The network feels they're strong enough on their own to merit airing, but not so strong that they could carry themselves through a full season in its own timeslot. Usually it'll get slotted in in between two big popular shows (The much desired 8:30 Thursday NBC timeslot of the mid-nineties was a huge spot for rotating midseason replacements being between Friends and Seinfeld) or replace a big show during a hiatus before being moved to its own timeslot to try and hold its own upon the former show's return.
