Forced Username Change

Why, with the change to Riot Accounts, were we forced to change our usernames? I had to do this for both my PBE (I have one of the old accounts that is actually separate from my NA account) and my NA accounts. I was given no reason why. It would be one thing if they told us "Hey, some other person has your account name, which I highly doubt they do, considering this stems back from an idea I had as a literal 8 year old child 13 years ago, or for some other reason. I've been using the same account name for the past 8 years, and now it was forced to change for absolutely no apparent reason, which really makes me upset, since now there's a good chance that I'll have to go through the "no wait that was my old account name, now I have to put in the new one" thing for probably the rest of the time that I play this game. It's just asinine, if you ask me.