Because all exchange platform need to the personal info.
Also I can't buy huge amount bitcoin and altcoins via the platforms.
You can achieve this on Binance and AFAIK they don't require that much information before you can trade significant amounts of money, say a couple thousand. Or you can head over to the Currency Exchange section of the forum and find someone interested in your ad.
But yeah, the safest and fastest trade is still P2P for higher-priced transactions. Just be sure that you're on a safe place and/or escrows are involved to avoid getting duped for your cash.