It is not difficult to agree link sharing programs are a no-no. They make the link trader wary. People do it innocently all the time.
Link sharing "In Action".
Link sharing programs are still around. They capitalize, by using the hook of improved link popularity, to lure people into their web (pun intended). Many are not forthcoming about the true effect of these programs. But, the traffic through the links from all the participating sites, in the program, is designed to bring traffic to a select number.
When over 500 backlinks gives a website decent linking power, while others do it with 20 links, it's not worth sending the traffic to low power linking sites. There's no inherent value in the links. The purpose is only for link popularity. However, the people, who run the program, benefit from the link clicks. It's a very skewed picture.
There's such an over-emphasis on linking power, other good reasons have taken a back seat. Perspective is lost.
Linking strategies.
Many linking strategies are based on what the original purpose of the site is. A large site focused on providing content and information is different from an e-commerce site focused on selling a product. They'll begin and evolve differently.
Conclusion.
Sites, for selling, link with other, like-minded sites. These websites are complementary, for exchanging traffic and getting sales. Content is added with the intention of increasing sales by informing customers.
A large information site may also bring revenue. However, by nature, it needs to have more of a connectivity with the rest of the web. Others are a combination.