when do you decide to repipe?

[Mario Am]

So I had one of my rental having many leaks issues that we needed to remove the flooring and repipe half of the house plumping (mind you - its concrete slab, such a pain.) while my tenant is occupying it. when I bought the property I didnt replaced the plumping because it seemed fine and house (70s built) didnt show really any leaks or issues. It was a fixer upper that I fixed only the electrical and added the HVAC. Had me thinking I wish I did replace it before moving in the tenant and putting in flooring.

On the other hand another rental that I did replace the entire plumping before moving in the tenant, I RARELY have issues because its brand new piping.

Had me wondering, when do you guys decide that you want to repipe the entire property before moving in a tenant? Assuming you cant see the entire piping and its slab? Is there a certain year that you decide that you HAVE to repipe it? Do you try to stick to buy houses built in certain years that the pipes should last?