Why can I never reuse a password?

I recently opened an outlook email account when I loaded Office 2013 onto my computer. Through various circumstances, I had a mix-up with the passwords and had to create another one, then it was not recognised and I had to create a new password again. I tried to use my original password and it was not accepted. Microsoft requires me to create a brand new password whenever I change passwords in my outlook account, even though I may not have used it for the account for months or even years. I think that Microsoft is going too far with its security. With all the passwords that I personally have to manage, I am trying to make sure that many accounts use the same password. Otherwise I can never remember them all. Please Microsoft, be more flexible with your password rules. We, your customers, are only human!