That is an incorrect expression, "Here are why" makes no sense.

Dear friend you need to ask your question in context. I think this is a part of a text but you haven't given us enough of the text to give you help you. ;D

I always came across "here is why". Althought "are" suppose to plural form of "is" my ears won't like it. "Here are why" sounds awkard to me. I think it is because we always say: "It is" and not "It are". And as you don't know what object/s is/are you talking about yet you always use singular. By object I mean grammar object. I think if you say: "I like icecream. Here is why: It is fresh and I love its flavor." It is perfectly fine. "You don't need to say: "I like icecream. Here are why: It is fresh and I love its flavor." Even thought reasons are two; before you show any possible awarness of possible plural you use singular and that is "is". But of course I am not native so maybe someone has better explanation =)

Americans always like to say "Here we go", "Here we are", "Here you go"... "Here" can be different meanings.."Here + be words,like is are...." = " this is or these are" "Here are why" = These following are the reasons... "Here is my phone number 1234567" = you can say it when you email or such situations to someone instead of "My phone number is 1234567." "Here we go" = we can say it when we are working on something together, and finally it is done. "Here you go" = we can say it when you deliver something to someone, like your friends ask you pass bottles of water, you give the bottles to them, and you can say "here you go" "Here you are" = someone was looking for you, and finally find you will say that.. .....Anyway, "Here" has thousand ways to use.. Hope helpful!!

Americans always like to say "Here we go", "Here we are", "Here you go"... "Here" can be different meanings.."Here + be words,like is are...." = " this is or these are" "Here are why" = These following are the reasons... "Here is my phone number 1234567" = you can say it when you email or such situations to someone instead of "My phone number is 1234567." "Here we go" = we can say it when we are working on something together, and finally it is done. "Here you go" = we can say it when you deliver something to someone, like your friends ask you pass bottles of water, you give the bottles to them, and you can say "here you go" "Here you are" = someone was looking for you, and finally find you will say that.. .....Anyway, "Here" has thousand ways to use.. Hope helpful!!