It doesn't happen that much at the end of the year anymore for jrpg's, so why not share this good message. Two jrpg's doesn't always sell that well, so it's nice to see this two milestones for Persona 5 and Sea of Stars.
We just heard in June that the P5 series stood at 9 million, so it's likely that Tactica sold a little under a million copies. For a smaller project being sold at full price, that's pretty good numbers for a JRPG. I'm sure they are happy with it.