First of all I’d like to acknowledge the existence of 3rd party tools for checking and sending EVEmail. CCP generally should not do what 3rd party developers themselves are perfectly capable of doing (often better), particularly when it has already been done. However, just as when CCP introduced fitting simulation in game despite the existence of far superior 3rd party fitting tools, I believe there is strong justification for the EVE Forums having EVEmail integration as part of its UI/UX.
A lot of forum discussions (often held in realtime) merit private messages between users instead of or in addition to discussions on the forums themselves (often times as a collaboration to the thread discussion), but these users - particularly those using forum alts that don’t actually log into the game - won’t be notified that they have received such a message unless they were already logged into the game or simultaneously using a 3rd party tool or EVE Portal from which to receive notifications. Most EVE players, however, do not use out-of-game EVEmail tools.
Currently the only way to ‘ensure’ this kind of private interaction is to tag users and say “I sent you an EVEmail”, which is awkward at best and often untimely in relation to the progression of relevant forum threads when the EVEmails get read and responded to, if ever. Forum users respond to forum notifications, but not necessarily EVEmails in-game or from 3rd party tools; incorporating EVEmail into forums brings EVEmail notifications to their attention so they can respond accordingly, and makes it more convenient for them to send EVEmails of their own.