Need Help understanding the Nothing at Stake Problem

Hi, so as the title says, i really need help understanding the nothing at stake problem, i’ve read through many articles and watched many videos, but still cant get my head around why would any validator produce two blocks on the two branches of a fork. Everyone says that a validator may do this to be safe from his block getting orphaned, but i cant see why this will happen if he produced only one valid block, this will resolve the fork and he will get his reward. So how can his block get orphaned if he produces only one block? I understand the part that an attacker may do this to double spend his coins, but i struggle to understand how the validators are economically incentivized to produce two blocks, after all, if a validator produces just one block, the other validators will vote on it, and the fork will resolve, right? Any help will be appreciated.