Comment by NoahZuniga

Making advertising non tax deductible has the effect of making it marketing ~20% more expensive, which would lead to about 20% less marketing. But not really. It doesn't really cost YouTube anything to play an add, so YouTube ads get 20% cheaper, and you see the same amount of ads.

Also this would be hard to implement. Tax law has a hard time discriminating costs. What if all the marketing is done by an Irish subsidiary?