It can draw people to buy on credit, thus stimulating demand. And fundamentally businesses are taxed on profit, and advertising is an expense, so if you start saying advertising isn't tax deductible, you start fundamentally changing the way corporate taxation works and opening up a whole can of worms. Adding a tax on advertising spend like a sales tax would be far less messy - but it would benefit brands with large existing recognition at the expense of smaller/emerging companies. Without advertising, warby parker would never have been able to grow, leaving luxottica unchallenged as the largest frame maker. You'd just cement current market leaders.