As someone who uses the same gmail address since 2004 I thought that's what everyone does. Then I've started selling software and to avoid collecting personal data I've decided to link licenses to email addresses. Having sold 10k+ commercial licenses I get to deal with email address related problems about once a day (email address expired, blocked, access was lost, the provider doesn't allow using it from current location, the company closed, the university doesn't let you use it anymore etc.).
Fortunately security doesn't really matter that much to us. Worst that can happen is someone gets to use additional license. We don't collect any personal information so there is nothing to leak. If that wasn't the case though and we had any kind of personal information linked to licenses I would really like to avoid using email addresses for anything. The simple: "Hey, my name is X Y, I lost access to abc@test.com address, can you please let me use another address" becomes a security nightmare.
It's one of the things you learn once you start doing something on a bigger scale. Some other things which I've learnt actually happen but never happened to me: SSDs fail, RAM fails quite often, a lot of stuff fails with some Windows settings that won't ever fail on 10 computers you test it on etc. etc.