In the past, you may have seen something called a paying URL shortener. This kind of website pays publishers to get visitors to an intermediate page with ads, after the passing of which, they can have access to the link that the publisher has put into the system or - shortened.
Firstly, I would like to tell you, that this kind of site is very profitable not only for the publisher, but also for the website owner, and because the market is not too saturated at this time, I would of course recommend you to create your own shortener, which I will make a tutorial for very soon.
Now, you may be asking, how do these sites make profit? Well, because of the fact that there is ads on the intermediate pages, the owner will receive earnings from direct advertisers - people with a business who contact the owner of the site for him to place their ads on his site and ad networks - sites that connect site owners, the person running the shortener, and the advertiser - person who wants his business advertised.
This, is where the profit comes into play. When the site owner receives money from the ad networks, he normally does not have to give that all away, because of the fact that he normally sets Publisher Rates lower than the earnings he gets, something like this:
As you can see, if he sets up the rates well, which I will also make a tutorial about, then he will have some amount from the ad networks that he can keep to himself and have a profit. In a nutshell, this is the reason shortener owners like to run the business.