Why does the TB calendar give GM shards?

Via the shard crystals you can get GM shards that are almost useless for TB. It take multiple months to form one and you’re likely to gain a three star. This is just my two cents.
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Comments
Personally I don't care about those shard crystals so don't feel TB are losing out anything
Even if they were Cav shards, they wouldn’t made any difference, since you most likely would pull a 3* or 4* once a month.
Also, the Cav shards calendar for TB sucks too. One crystal per 14 days is too low. This should be minimum one crystal per 7 days.
Calendars, apart from the t5bc, t2a and the units are mostly a joke.