I guess $1 is the standard among all the centralized exchanges for placing minimum purchase orders because I have checked a few like Kraken, crypto.com, bybit, and coinbase so that is actually the minimum amount you can buy irrespective of the crypto unless you do f2f trade.
By "f2f trade" do you mean "P2P trade"? It's true that there are no centralized exchanges with a minimum order of less than $1. It could be a result of high network fees from most popular cryptocurrencies. Coins with dirt-cheap fees like XRP and SOL can be traded for less than a dollar, though. It would've been great to invest in these coins with spare money just like you would do with stocks. Maybe someday, right?
I think Gate.io allows for buys from 1$ and above. I have bought some tokens in there for about that price.
I was actually shocked to know that I could buy a token for a dollar, I thought the minimum buy is $10 just as binance makes it seem but I later realised that other exchangers allows for less than that but I only know about gate.io for buys from $1
It's just like Coinbase, and Kraken. They have a minimum buy order of $1. Nothing less than that. A pity, because this would've allowed us to make microinvestments for long-term profits. Sort of like how it's done with penny stocks these days. Maybe high network fees have something to do with this?