I think you have to look at it relatively. You ue a tiny bit of marmite in comparison to jam or peanut butter. It is potent so you spread it thinly and it still tastes insane. One pot lasts a long time, hence the pots being small, and in comparison, expensive.
As a Marmite nut, I have to disagree; it tastes best when spread thickly. But then I also eat it straight from the jar with my fingers. Yes I know, I am weird...