Because your Pricing Group column doesn’t have a relationship with Sales table.
If you want your measure to work in the current scenario with the current arrangement intact then use:
Total Sales =
SUM( Sales[Total Revenue] ),
VALUES ( 'Groups For Pricing'[Pricing Group] ),
Or just create a relationship between Sales and Pricing Group and then everything works, but you still will have to make a change to the calculated column’s code in order to be able to create a relationship, otherwise Sales table would depend on ‘Groups For Pricing’ table for the Pricing Group column and ‘Groups For Pricing’ table will depend on Sales table for blank row, creating circular dependency.
Pricing Groups =
DISTINCT ( 'Groups For Pricing'[Pricing Group] ),
'Groups For Pricing',
Sales[Total Unit Price] >= 'Groups For Pricing'[Min Price]
&& Sales[Total Unit Price] < 'Groups For Pricing'[Max Price]