The reason why store bought buns are so soft is because the store bought buns are made with additives that help maintain the softness and shelf life of the buns.
Also store bought buns are made with the use of specific ingredients and baking techniques which also help maintain softness and shelf life of the store bought buns.
Commercial bakers who make store bought buns often use certain types of flour, fats like butter or oil and sugars in the bun and bread recipes which leads to a softer texture.
Store bought buns and bread also are baked using precision and consistent baking methods that produce a consistently soft bun and breads.
Store bought buns also have additives like dough conditioners, emulsifiers and enzymes which are used to enhance the softness of the buns and bread which also extends the shelf life of the bread.
Store bought buns and bread often use enriched dough's which include ingredients like butter, eggs and milk which result in a softer crumb and crust.
Other additives like amylase and calcium propionate as well as chlorine dioxide are also used in store bought buns and store bought bread to prevent staling of the buns and bread and maintain softness.
Homemade buns rely on the use of natural leavening and aging for softness and store bought buns utilize the other techniques to get the softness.
Restaurants keep bread warm by using heated steam drawers as well as commercial drawer warmers and heat lamps or ovens.
Heated steam drawers is how most restaurants keep their bread warm.
Some restaurants may also keep their bread warm by wrapping the bread in foil or towels or storing the bread in baskets with heated stones or rice.
Keeping bread warm during transport can be done by using insulated bags and boxes.
Steam drawers maintain the warmth of the bread as well as the moisture in the bread and keeps it from drying out.
Ovens and warming drawers in restaurants can heat the bread and maintain the breads temperature in specialized warming drawers.
Commercial drawer warmers are also an essential part of a restaurant and catering business which ensure the bread stays warm and ready for serving.
Heat lamps are sometimes used to keep plated food including bread warm until it is served.
Wrapping the bread in some foil or towels also helps to retain the breads heat, especially during storage or transport.
And bread warming baskets can be lined with napkins and used along with a heated stone or rice to maintain the warmth of the bread.
Some restaurants also have temperature and humidity controlled warming drawers built into the waiter's stations where the bread is kept warm and moist before it's served.