>contracts with unlimited time periods non-binding?

I've noticed in countries with Natural Rights frame works for their law that typically contracts that commit /an individual/ to work when it's not "bonded" in some way are interpreted as slavery and nullified.

e.g. If I agree to get paid $100k lump-sum today to work for you for 10 years at no more compensation, and at year 2 I decide to renege on the contract, no Natural-Rights framework court is going to enforce that.

But if I sell my house to you (relinquishing ownership to you for an "unlimited time period") and I try to renege on the sale, it is going to be enforced.