>>211958753mini-series and anthologies are a thing. shit like american crime story, manhunt, true detective, american horror story, etc. have been quite popular throughout the last 10+ years.
in the case of yellowstone they decided to keep running it organically which meant they could introduce and experiment with plotlines as they went along to see what the audience enjoyed and emphasize on that or drop those plots that nobody wanted.
it also allowed them to see which characters are liked which then justifies spin-offs once the main series stalls or ends.
of course there's still problems with it, as you said - the continual squeezing out of runtime even if it doesn't make sense to repeat the same shit over and over or making it ridiculous.
they should have stuck to their original outline, if they even had a proper one, and kept introducing side characters on the go.
instead they kept dragging it on for at least 2 seasons longer than necessary