[coffeeaddicted]

Wikipedia competes with other companies not just on market share and money, but even more on attention from people actively supporting it by editing the information. I see no immediate gain they could get in market share by making money with ads as they are already having the biggest share of any encyclopedia with their current way of working. But I'm rather certain they would lose a lot of editors and would even give a competitor a chance to gain those people. As little as many people might care about seeing Google-ads, no one helps Google for free. Swarm driven websites have to care about attention from people far more than about money as long as they are able to cover their costs (and they are able to do that as long as they have the swarm behind them).