There must be some huge incentive for Reddit to push users toward the mobile app. Most likely, the app allows for higher or more accurate monthly active user counts and enables more targeted advertising, both of which are critical to increasing advertising revenues.
Reddit is in a difficult spot because they're mostly an ad-supported business but their users are vehemently opposed to advertising and any forms of tracking. They have to tip-toe around all of the advertising and user tracking that they do. Strangely, their users mostly seem to give them a pass on the tracking. Their users are relatively trustworth, viewing Reddit as far more trustworthy of a company than Facbeook, despite the two companies having largely similar business models.