[ghaff]

>Budget, maybe?

Budget and the revenue from a hit.

Making a hit is such a crap shoot that depends on a lot of things including what basically boils down t luck, i.e. it grabs the limelight for whatever reason. So when something does become a hit, there's a lot of pressure to just keep things going.

- The network likes that they have a predictable money-making show.

- A lot of fans will continue watching out of habit/duty.

- Many actors and others associated with a hit show may think (often for good reason) that they'll likely never see as good a payday again.

It's also worth noting that shows like Breaking Bad and Game of Thrones still had relatively niche audiences compared to a hit on a major network. Probably makes it easier to plan for a fixed length.

You do see some of the same effect in, say, genre fiction though. There are a lot of interminable series because they have a built-in readership.