Unfortunately, nothing is really free* in this world, including this website, and my other websites.
Currently, I pay for the domains (+anonymous registration) and hosting out of my own pocket, in addition to some small but generous donations that I receive by people who would like to contribute a few pennies to my Hypixel-subdomain. Now, don't think that I am desperate for some extra cash (With a small job / web development task I can easily afford one year of all hosting costs), but I would appreciate it that the services could 'pay for themselves' – For which ads seem the perfect solution. It'd be kind of (in my honest opinion) a waste to spend most of my earned cash back in this website and everything that comes with it. Note that I'll also begin studying near the end of the year so that means I'll need even more of my money (and the government's) to spend on important things such as my tuition fees.
Now, don't take me wrong – I too think that advertisements can be frankly annoying or outright messed up sometimes (things like forced redirects and popups). Luckily, nowadays these things are not so common and especially at big networks such as Google's own one these things are not even allowed or can be disabled. I don't doubt that if at some point I manage to get advertisements on my website, they don't pay back for the whole site for a year, but I don't see that as a problem. Just like now, I'll continue to pay for the rest out of my own pocket. Also, regarding placement of these ads, I would most likely place a banner ad near the bottom of the page or somewhere where it wouldn't get in the way of the main content, especially on mobile devices.
*Most materialistic things aren't, anyway