Surely, Thailand has enough different supermarkets, no?
Lotus's
Big C
Makro
Villa
Foodland
Tops
MaxValu
GourmetMarket
Rimping
FreshMart
Any more?
Hardly a monopoly.
Thailand also has so many fresh markets to choose from too (for food) and there's always 7eleven, Lawson, and Jiffy for your toiletries etc. etc.
I am just waiting for Costco to enter Thailand. They are already big in Japan, Taiwan, and starting to expand in China.