ELI5 US- Health Insurance - why do I need a new account each time I come back to a brand of insurance? My job switched to Cigna which I had at an old job but need to make a new account.

Please ELI5, this wasn't accepted over there for being too specific. Why can they not just apply my NEW benefits to my existing accounts, and remove the old stuff, its tied to info like my social security number and DOB. I probably have 7 cigna accounts now from over the years. I'm running out of usernames that I'll remember.