Given your profile shows all your comments and submissions (and would likely still show them if only the name was changed), I'm not sure what the big deal is here.
You learn to recognize the names of active users that post in threads you're interested in. I shouldn't be able to ditch that recognition but keep my karma, and you shouldn't have to look through my history to see if I'm someone you previously recognized.
Eh, maybe I don't see it. I mean, I use a lot of internet forums running scripts like XenForo and IPB, and those let you change your 'display name' whenever the hell you like. Yet I still recognise everyone perfectly fine. There are people on my forums that change their display name, avatar and signature on a weekly basis. I still recognise them just fine.
Same works on Discord too. There you can change your name whenever the hell you feel like it. Again, doesn't stop most people recognising you.
Perhaps not in that case, but regardless, this is the kind of thing should be designed in deliberately as a feature (with an option to bypass it under special circumstances), rather than some accidental/arbitrary technical limitation just because the dev team didn't bother to implement the ability to update the field for whatever reason.
