These letters matter a lot to kids. I sent my video game idea to Nintendo as a little kid and I had the same reaction seeing that envelope from Nintendo in the mailbox addressed to me. I think it was also a bit more special pre-internet as these companies felt a bit more magical and mysterious. You can only read about them through video game magazines and see their names in the credit scenes at the end of the games. Unless you were one of those weird kids that called Nintendo Power helpline of course!
I remember also receiving that weird VHS tape from Nintendo in the mail: https://www.youtube.com/watch?v=rJzIc_c1PvE
I have no idea how I received that, but it was so cool!