Why are Paxful transaction fees so low?
Paxful has withdrawal fees, as any other exchange or Bitcoin service that I am aware of: sending bitcoin is costly, so it will be very unlikely that some company will send you btc without charging a fee.
This is from Paxful Fees webpage:

So Paxful charge you with 0,0004 btc if you withdraw more than 20$, which is usually more than you have to pay to send a standard transaction with Electrum.
As a side note I tell you that in the last few days Bitcoin network fees went crazy, a sharp hashrate reduction has created a long queue of pending transactions and sent commissions to the highest level for 3 years now; so right now you can pay more than 0,0004 btc but it's a very rare case as you can see at this historical chart: https://jochen-hoenicke.de/queue/#BTC,all,count