Users name fixed to only admin

Why was the users name fixed to admin only this makes no sense at all as many different makes of router use this users name but allow one to change to it for security reason and that's on their home routers. Changing the password is standard for all routers so why leave one layer security taken away from the Netgear router's like the r7000 and others from some of the postings I have seen.

If I were a hacker who wanted into someones router I would love the fact the users name was fixed to admin the password would the hardest thing break with both unknown the job would be much harder.