Why do I need to leave the country before I can open my tax free consumables? [duplicate]

They want to tax goods you consume in the country.

For goods you consume somewhere else you have a real option of buying them somewhere else too; and faced with the possibility that you'd rather do that they prefer letting you not pay the tax and still buy in Japan; at least that will contribute to the local economy.

But for something you use in the country you don't really have an option to go elsewhere, so there's not as compelling an argument you should get out of paying taxes (usually luxury taxes on some kinds of goods).

Because the fact that you are exporting the goods is the critical fact that makes them tax free. If you consume goods in Japan, they're no longer legally exempt from tax.

The requirement to pick them up at the tax-free stand makes it less likely that people will circumvent the tax law by buying tax-free goods for improper purposes.