According to me, Where the Nofollow links exist because we don’t want every single webpage or link to be something a search engine crawls and ranks. So, no-follow link attributes tell search engine bots not to follow a certain link. These types of links are still clickable for a user, but not followed by a bot. On the other hand, all other links could be considered do-follow links, even though they don’t have to have special attributes to tell the search engine bots to follow them—the bots will by default.