Much like with trade, advertising isn't necessarily a zero sum game. Nor is it the same experience for everyone. I suspect your perception of advertising is distorted by your own context.

A high income individual might see advertising as targeting their disposable income and attempting to get them to spend more of it... because that's what will really move the needle for the advertiser with that customer. But it's a totally different experience for advertising's impact on low-income consumers.

Amongst lower income folks little if any of their spending is disposable income; that's not going to move the needle for an advertiser. What might move the needle is the non-disposable income, particular for staple consumer packaged goods (CPG) like food, clothing, cleaning products, etc.

The goal isn't to get lower income folks to spend more of their income at all, because that isn't an option. The only way to reliably get low income consumers to spend more money is to give them more money to spend. In most cases, all or almost all their income is going to be spent even without advertising. When you are hungry and on a limited budget, an ad isn't going to convince you to spend more money on food, but it might change your mind about what you decide to eat. So advertisers aren't trying to convince poorer folks to spend more of their disposable income, but rather to choose to spend their non-disposable income with the advertiser instead of a competitor.

While advertisers may be attempting to manipulate an audience, lower income folks aren't so vulnerable. You can show them as many ads as you want for yachts, they aren't going to buy one. The more vulnerable audiences are those with more choices, not fewer.

Stronger players in a market tend to be able to afford more on marketing, which can mean that advertising ensures those consumers are aware of the stronger players in the market. Consumers consequently have learned to treat extensive marketing as an easily detectable proxy signal for that strength, which, despite its pitfalls, is often more reliable than other signals (unfortunately, targeting can undermine this a bit by making an advertising seem more pervasive to a targeted audience than it really is, but overall it remains more true than not).

Brand awareness advertising in particular tends to increase the importance of providing a successful product experience to those lower income populations, because those populations are more risk adverse to a disappointing experience (one can't just buy more food if the stuff one spent the last of one's paycheck on turns out to be terrible). Consequently, even though lower-income consumers might have a lower expected customer lifetime value, an advertiser might be more concerned that a negative experience with them, as the damage to the brand image might be far more lasting.

If you have a non-staple CPG good, your revenue isn't going to be coming from consumer's non-disposable income, so you're going to naturally disenfranchise consumers who don't have much if any disposable income. You won't care about their needs or their complaints. Maybe if you are creative, you might increase margins on your product so you can find some way to give away your product to those without disposable income, thereby having people with disposable income subsidize everyone else. Unless...

...you make your product ad supported. Now you might derive much of your revenue stream by appealing to a customer base with no disposable income, because you are getting paid by an advertiser with a product that might target non-disposable income... and even if those consumers are being influenced by the advertising, they aren't going to be spending money they wouldn't spend anyway (not a choice available to them), and while it is far from certain, they are more likely to be getting better value for that money.

So one can argue that advertising makes advertisers and ad supported products more sensitive to the needs of lower income populations who do not have disposable income.

BTW, how are ads incentivizing user-focused development? Look at the Top 100 apps in any apps store, and tell me they're not virtual clones of Clash of Clans, Plants v Zombies and Candy Crush. Every developer is heeding self-interest first.