The reason why we shouldn't cook food in a pressure cooker is because it can lead to overcooking and a mushy texture, loss of nutrients, flavor limitation, safety hazards, inappropriate for frying and can be difficult with timing.
When cooking foods in a pressure cooker, it's impossible for you to add ingredients during the pressure cooking process, and the time that is required to pressure cook and for pressure to build and release can also be inconvenient for foods that you need quick cooking times for.
If the pressure cooker sealing gasket is old or the vent on the pressure cooker is blocked, it can lead to the pressure cooker malfunctioning and can lead to hot food splashing out, which can be dangerous.
Pressure cookers are also not good for frying foods in such as French Fries, chicken etc with oil as the high pressure and steam will cause the hot oil to splatter.
And because the pressure cooker pot is sealed, it does not allow for evaporation, which can result in blander flavors and prevent sauces from thickening up.
And although pressure cookers are efficient, the high temperatures of the pressure cookers can destroy heat sensitive nutrients like folate and Vitamin C, which can make the foods less nutritious.
And cooking delicate foods like leafy greens, soft vegetables and pasta in the pressure cooker can result in the delicate foods easily turning into mush.
And cooking foods like eggs in the pressure cookers can result in the eggs cracking and create a mess.
Pressure cookers are great for some foods, like soups, stews and tough cuts of meats as long as the pressure cooker is operated properly and safely.
But pressure cookers are not good for all kinds of foods.
Even many top chefs don't use pressure cookers for reasons which include.
They are just hard to control and adjust, as compared to techniques chefs like.
Chefs are very used to constantly tasting and making small adjustments.
The braising liquid doesn't reduce in a pressure cooker, so you need a lot of time after to a usable sauce out of it.