Putting the default fan speed at 90 makes for foo foo manufacturing process and preys on the ill informed. Diving into the linux portion of the router should be done anyway(com'n Openwrt would be the reason for "switching" from a main stream gui-based router), but default settings set from the factory creates a perception of deceptive business practice to run down hardware early for the comsumer to just get another router sooner to waste expenses.
You might need to check the forums about the life expectancy of running at 90C. Here a the link for the source of the reference and credit to Johnex for the graphs. Johnex.