That's precisely the issue. It's only a good reward for people who've been playing for 6 whole years. Any mobage will have an attrition rate, and to stay alive, it needs to attract new players. A fragment per day would be about 30% less significant as the retroactive +10 per 50 days from 3rd Anniversary. 10 SQ per 50 days for 3rd, and 7.14 per 50 days for 6th.
The message that sends to new players is positively awful. Playing from start to 3rd Anniversary, an era of constant new content (and of Shiokawa) would get you more immediate quartz when its reward (3rd Anniversary) came out than playing from 3rd Anniversary to 6th Anniversary, which has seen constant shouts of "dead game." A quartz bonus--and a quartz bonus alone--would essentially be adding insult to injury, admitting that the last three years have been unrewarding and then straight-up mocking players who joined during them.
Which is why that's probably exactly what Kanou will do.