Saying "you won't get anything of value quickly is a deterrent.

Security doesn't need to be able to completely stop an enemy. It just needs to make it not worth the effort

There is no invaders

I mean I hope so. There never are until there is

If you wanted to educate us you should post it here, it would work better

They are banned for the same reason the use of cluster munitions are frowned upon. The problem of being left behind after deployed during war time as they continue to cause horrific civilian casualties which is a huge a big problem for a country trying to recover from war. Particularly if they were deployed inside a country to defend what was then the front line or a fortified location like the outskirts of a town or village.

However if you find yourself in the unfortunate position of having an aggressive neighbouring country where you share a large land border who has broken peace treaty promises repeatedly and is repeatedly making threats about invading, then putting landmines along your border is a VERY effective way to deter and slow down an invasion.

I wish that we weren't in a situation where countries felt it necessary to deploy landmines for border defense but here we are.

And how many die in wars if someone invades?

Wrong. If nobody invades, the mines don't get laid out in the first place.

If it does come to that, the positions are marked mapped and they will get cleaned out. The reason for the treaty was that in some places mines were just spread willy nilly.

I still haven't seen your explanation for how this is actually an offense, but keep moving that goalpost 👍