> I could see maybe 20 years after death being reasonable.

And another person sees 10 years as reasonable, another as 30 years. Ultimately, our life-spans also change, so what works out today, might not work out in 30 years.

What about after the last direct decedent is no longer alive? Grand-children might not care that much, but it's unlikely your children wouldn't care about how others use a name associated with you and indirectly them.