I think this is a function of shows knowing what they want to do early on, but also knowing that there's a really good chance that they'll be unceremoniously ax

I think this is a function of shows knowing what they want to do early on, but also knowing that there's a really good chance that they'll be unceremoniously axed, so they don't invest up front in longer-term arcs. They get picked up for subsequent seasons, go soap opera, and then just rest-n-vest.