Technically there are no reasons why they simply cannot put out in game notifications. We had them in Dust all the time, and before I quit that game last year, we even had a running ticker with updates if we needed it. Every time we signed in, there was a full description of the most recent hotfix/patch along with any new information that was relevant to players before you went to your character selection screen.
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Apparently, they said that the only way that they are able to push in game notifications is through game updates.