E-Addys

Why do some people change their email address all the time? I write an email and wonder why nobody is answering me. Weeks later I go through old emails and find out that they changed their email address month ago. Am I supposed to check if the email address has changed each time I get an email? Why do they change it at all? It’s not like when you move your address change. I am still using my first email address from 1999! Well sometimes it might be necessary to get a new one for some reason. So can’t they just tell everyone? I don’t blame someone for changing the email address but for not telling me and expecting me to notice by myself.