I totally agree with you. I have a friend who is entirely the opposite. She's really into Masterpiece Treater type stuff and she's constantly complaining about 5 episode seasons and series that only last a few of those seasons.

>please don't string it out for 7, 8, 9 seasons

Especially historically on broadcast TV, there were a lot of incentives all around to continue to milk a cash cow with a core audience who would watch it for the next 20 years given the opportunity. In addition to the networks, I'm sure many of the actors and others involved in a long-running show realize they'll probably never have as good a meal ticket again. So screw artistic vision.