It’s primarily due to the lack of seasoning, if you are sick enough to be in the hospital hopefully recovering the last thing they want the food to do is delay the recovery.
That means no salt, sugar, pepper or any other seasoning to enhance the flavor of the food
At least for me I rarely use salt as a seasoning but almost always use seasoning and often times pepper flakes or hot sauce take all that away and the food is bland and tastes completely different
(lack of seasoning)
That was my primary guess.
It’s such a weird taste with hospital food.