In economics there is a concept, profit maximization, where it is determined at which prices the products will, well maximize profits, by taking into account marginal changes in supply and demand. I would be very surprised if the big ad companies didnt have a few economists do the calculations.

https://en.wikipedia.org/wiki/Profit_maximization?wprov=sfla...

I'd be even more suprised if the profit maximization point when prices and the demand for ad spots were both down involved an even higher supply of ad spots for sale.

Finding the right level to decrease supply by would be a tricky calculation to get right, but in no way could the right move be to further flood the market with supply.

You have to remember economics is a model and not exactly how reality works, there are many examples where you will find the supply demand curves arent linear and there are also other things to take into account. Companies can artificially move the demand curves, for example the ad companies can change the quality requirements of what ads they allow, creating more demand. These calculations are best done with real numbers and experiments, kinda like A/B testing and I would guess that the ad companies have such infrastructure