The reason for that is the option is only available on certain heads, not all of the heads you can choose from when customizing a doll. So you would go here: https://reallovesexdolls.com/enhanced-mouth-add-on/ and add the option on to your order.Additionally, if RLSD is unaware, their website doesn't currently allow the option of selecting this option during the custom doll selection, only during separate head purchases.
Big lips as mentioned in some of the posts prior are not a feature of this enhanced mouth. The enhancement is a tongue and uvula addition to the inside of the mouth. The face will still look the same as it always has otherwise.
This is a new addition straight from the WM Doll factory. We have not personally seen it ourselves yet to comment on how well it functions. A real tongue is a muscle and this obviously is not.
And as someone asked also... no, the tongue does not stick out of the mouth, it's fully inside only.
UPDATE from WM Dolls: due to the popularity and amount of orders for the enhanced mouth, coinciding with the Chinese New Year holiday... orders with this enhancement selected will be back ordered until late February, after the holiday.