I have had the legacy account for years.
Since you have had this account for years, maybe it is an update that is going on, thus requiring you to provide current data. Basically, most exchanges now are requiring for KFC, so that is possibly what this is.
Not all exchanges, some still accepts traders even without KYC, I have account at Binance and Kucoin but I can still trade without KYC.
It could matter depending on the size of money you trade, but in my case I'm just an average trader so I don't play with huge money and I'm okay with the current set up.