In the mainline Pokmon games, Diglett is not a starter or a legendary, but it plays a significant role due to its unique typing and ability to learn moves like Dig and Earthquake, which are particularly effective against Electric-types, a bane for many players' teams
The inconvenience of shipping to a third party is nothing compared to losing a valuable card to a scammer
While it wont have cost any more in shipping (the Pokmon Center is unreasonably good on this, waiving shipping costs for purchases over $20), its going to be such an epic pain in the ass for the scalpers, as their every shipment arrives with this enormous extra box of stuff they dont want or need, and most of all, cannot resell
It remains to be seen how much of this flagship product gets printed, but suffice to say any valuable cards opened from the set has the potential to remain relevant for a long time