None of the Barkleys had a Love Interest that Lasted More Than 1 Episode

That's a good idea on that but it's a bit different in practice. Big Valley was what was known as an "episodic show". Episodics are individual stories unto themselves. They tell a full story from the beginning to the end and you don't have to watch the entire series to keep up. Serials, on the other hand, are one long story told in half hours or hours that are part of the one long story. Wagon Train was an episodic. Big Valley and Bonanza, too. Gunsmoke, Laramie and all the rest of the westerns, too. Soap operas are serials. So what does that have to do with anything? Well an episodic has a set cast that's fixed in stone so to speak. That cast is the entire paycheck for the company and they're the entire permanent work force, too. If they bring in even one more person and keep them, the show becomes a serial and the cast collecting regular paychecks grows, too. 1/8th of a set pot of cash is a good paycheck. If you divide it by nine, with a set amount of cash to work with, the other's checks get cut and you can lose your most important actors. Star Trek created the meme....the infamous "red shirt" character. Any red shirt character introduced in any episode tended to die by the episode end. Fixed cast getting a fixed amount of a paycheck....temp cast getting temp worker's wages who appear and then disappear by the end of the hour. As in all work, you want to keep the full time expensive workers to a min and use cheaper part time workers.