In December of 2016, Google announced that they would be shutting down Contributor and replacing it with a better alternative. An alternative that was due to launch in January 2017. However, Google has officially shut down Contributor and is sending out refunds as we speak. Currently, the alternative is not yet available, nor has it even been announced. Obviously we still in the middle of January, so there is still time for Google to launch the alternative. But as for now, users are stuck with ads.
Google Contributor was launched as a way for publishers to still make money off of their own content, but users don't have to see ads. With Contributor you would pay an amount you wanted each month, and for that amount, you wouldn't see ads on some websites. The publishers that you visited would get a cut of that amount you paid each month. Depending on the amount you paid, depended on the amount of ads you'd see. For instance, the more you pay, the less ads you see. Ads have become obtrusive and many users have resorted to using ad blocking measures. That's not a good thing for the open web, as many websites make revenue from these ads, to keep the lights on. Thus Google debuted Contributor. It was never a popular program, but it was a good way to fight ad blocking.
Currently, there's no word on the successor to Google Contributor, but we should be seeing something announced fairly soon. It's not uncommon for Google to debut a new product and then kill it off shortly after. Google has many, many products that they are working on, and some work out while others don't. So while it is sad to see Contributor go away, it can't be all that surprising. It was a great idea and hopefully the successor will work even better than Contributor did, especially for those that dislike ads and don't mind paying a few bucks per month to get rid of some of the ads - especially the most intrusive ones. The Google Contributor website is now showing a 404 (but there is a page for signing up which is disabled and it tells you why it's disabled).