Surface-level: the API price hikes are at a glance meant to force out third-party Reddit interfaces. To speculate, this is aimed to funnel users to Reddit's official application. I can say that because the mobile website is getting crippled over time to "encourage" users to use the app.

Deeper-level: it is reflective of Reddit corporate's attitudes towards its users. They are gearing for an IPO, so they want to tell investors that they will be profitable (read: milk its users, monetize everything, remove convenient features if it will mean profits, etc.)