Way back in the 90's I lost my demon account due to a mistake with billing. It caused total havoc for me and I lost a lot of grandfather rights to sites you simply can't get into now. At that time I took avoiding action. I have my
firstlast@yahoo.com, but I don't use that much, I just squat on it. I have my own domain via what was yahoo small business but is now Verizon. I also have two gmail accounts and one hotmail account. One Gmail is for the phone stuff where they demand it. The Hotmail was kept for Skype but I just ditched my skype subscription because they pulled Skype To Go which was all I used. I'm not sure if I want to kill it now or not.
I have one more account which is an office365 business account (you probably all use home). It is for my business communications and pretty much nothing else. It will get closed in a few years.
My Orange ISP mail is redirected to my Verizon business mailbox. I will never use an ISP mailbox as a main mailbox again. Almost all account recovery procedures are against mailbox and/or phone. In the case of the demon mailbox my phone details were also out of date and I never gave a valid DOB in those days. Much vindicated by the number of systems penetrated over the years.
Whilst my use cases are extreme, the message is the same. ISP's give you free mailboxes to make it a pain for you to move to another ISP. Which is all you need to know for why not to use them.