> are in a position where they wouldn't be useful.

No such country exists. So long as enemies are likely to put boots, wheels, or tracks on the ground in your country, landmines are extremely useful, extremely cheap, and extremely effective.

The point is that almost all of the signatories considered themselves to be immune to a "real war" in their futures at the time they signed. E.g. basically all of the European signatories assumed that the end of the cold war and existence of NATO would ensure the end of any possible threat. Given that assumption, as obviously flawed as it was, signing on to a ban was cheap PR (literally cheap, too, because it meant they could divest those weapons and their delivery mechanisms to reduce defense expenditures).