No, that's odd. Supply is not much restricted per route.
There's simply a pricing model where a more convenient or luxurious travel intiniary is more expensive. Only temporary popularity shifts could do a supply/demand price run, otherwise larger airplanes generally lower costs per passenger, and running more flights on the same line is likely a reduced effort and risk than having more lines.
Low-performance or high-variance lines could be higher priced due to having to pay for empty seats (on the same line of flights) but I believe this is not usual. The remaining passengers would be fewer.
I should think air travel would greatly improve with better customer-risk-treatment (e.g. no security - more like busses) and a 'ticketing model' that's as complicated as buying train tickets. Perhaps then we will see some more imaginative forms of air travel.