There are cases when a player is busy or travelling for a few days. Sitter function is anyway active only after 12 hours of player not online. For such extended period of inactivity, It makes sense to reward the sitter with a portion of money and prestige.
The sitter function is anyway possible only upto 22 days in normal worlds. Ie less than 2 ERAs. This can prevent inactive accounts being misused for sitter rewards long term
It's 30 Days in a normal world, 15 days in a X2 World and 8 days in x4 World.