But... They *did* ignore it up till now and them getting their own product ready.
No. They didn't. They found out about the site near the beginning of January, and then probably spent time cataloging the points of infringement on the site so that they could provide it to the owners of the website. Once they were completely cataloged, they sent off the C&D. Allowing for time for mail delivery, writing of the letter by legal staff, and time by WotC staffers to ID all of the violations of IP, this is pretty rapid turnaround time.
edited timeline to correct my error
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