My wife worked for a company that was heavily reliant on generating leads from ads. They had lots of real time monitoring of conversion rates to make sure they were actually making more money than they were spending on the ads. They would have to turn ad channels off all the time because the return on ad spend went negative.
So my conclusion is that ads can be somewhat effective for companies, but if they don’t actively monitor and control the performance of their ads, they’re probably just burning money. A lot of companies seem to advertise because they think that’s the only way to grow.