Everything comes down to money. Companies pay other companies to showcase their product. Without ads, how will GPT and PTC website be able to pay it's users? The importance of ads is to sustain free to use services. I know many site who have free to use content and vowed to never put ads on their website, but are in a constant struggle with paying server cost. Like Wikipedia for example, who don't run ads but ask for donations to cover server cost. Although they are success with covering server cost with donations, some websites aren't as lucky since they don't have the popularity as Wikipedia.
Everyone could be a marketer. For example "referrals" and Fusioncash. Although it's good to get your friends to try out fusioncash and earn money, but don't you think that what your doing is an advertisement to fusioncash? It's good that you and your friend is able to earn money by a referral system, but isn't it the same as how companies pay other companies to show ads (different scales but mind blown)
To limit the amount of ads you get per day you can use a DVR and skip through the commercials, use ad block when going online, instead of reading newspaper/magazines use the internet (with ad block... but remember the internet is killing newspaper, magazines, and books services), and outside ads you turn the other cheek.
Although I am playing Devils advocate, I can agree that a good majority of the ads are annoying and malicious. I love ad block and will use it on certain sites that provide (or prone) to malicious content, but I will be happy to turn it off and view ads from fusioncash, swagbucks, and twitch tv because it supports them
TL;DR Money is money. People and companies can't keep paying out of pocket to cover the expense of running free to use content. Necessary evil