It decreases the risk of failure but also corrupts the product signal. You can't get a truly clean read on the product/market fit with constant advertising since you're effectively externally subsidizing product adoption.

Or, maybe you aren't subsidizing it and just tossing money in the wind...and that's the problem, you have an x +/-/*/^ y effect and can't separate the two.

So the advertising becomes "locked in" because it was never extricated from the rest of the product and it becomes too much of a risk to pull it.

Some people try to isolate things and figure it out but it's not really possible, externalities change, contexts change, needs change, advertising happens on the sneaker net without your knowledge... It's a real bitch