Oh very true... but it also has at least 18" of height as well. Since BTS get all their heat from above, you need to be able to get the lamp close to the basking surface. The higher the tank, the harder that gets.

And 36x18 is the smallest minimum they can handle. It doesn't give them much room, and they burrow a lot. Longer and wider is always best.

36x18 for a bluey would be like keeping an adult beardie in a 20g. It could be done, but wouldn't be much fun for the lizard.