Hah, I had the same realization about landmines. Along with the other commenter, really it would be better to add intelligence to these autonomous systems to limit the nastiness of the currently-deployed systems. If a landmine could distinguish between a real target and an innocent civilian 50yrs later, it's be a lot better.
Many landmines disarm after a while.
It's weird that people still think that the people who's job it is to kill people, or make things that kill people, really care about people more than the killing part. They don't give a shit who blows up, as long as no one comes knocking on their door about it.
A landmine blowing up the enemy civilian 50 years later is probably seen as an advantage by the force deploying them. A bit like "salting the earth."