A loaf of bread is discrete and countable, a bread bun is equally separate and distinguishable. These therefore are countable nouns. There are exceptions, but bread itself *generally* is not countable as we do not consider it as a separate and distinct unit that can be counted. We imagine 'bread' as more a general description. As an example, think of the uncountable noun 'furniture'. 'Furniture' describes 'chairs', 'tables' that are separate and countable. 'Bread' is similar but with the component countable nouns being loaves, buns, etc)

You've gotten some good answers to your question. I would like to gently point out that the way you asked the question is not grammatically correct. It should be, "Can anyone explain this to me?"

Butter is the same way - uncountable. "How many butter?" does not make sense, but you can say "How many sticks of butter?" or "How many tubs of butter?" Though in a recipe it may say "10 grams of butter" or "two tablespoons of butter". In that case the quantity is of the grams or tablespoons which measure the butter.

I think the confusion for bread is that people often do not use the full name of the item. They may say "I want bread" but what they mean is "I want a slice of bread" or "I want a loaf of bread". "Please go to the store and buy some bread". The unspoken assumption is you want the person to get a loaf of bread (if that is what your family often buys). If you were given that request, you could respond and say "how many?" or "what kind?". Truly what you should say is "how many loaves?" to be clear. So you are right, bread can be confusing when there is laziness in the person speaking.

thank you