Most likely they didn't want players to exploit the longevity of food. Let's say for gathering. Player X just need 30 Gather and this food cost 5k, however the unspoiled node is only up every 24 game hours which means he can only use the food once.

In theory if the timer stopped when logged out that 30 min food could last the player 4-7 unspoiled node attempt if he could just log in and out, sparring time to regain GP or using Cordials as needed.