Two things are involved
1. Either the exchange doesn't carry out any due deligence to ascertain if such projects are legit or
2. Their ieo fee is little to nothing
if the exchange was a top exchange they should attain their softcap at least
But it proved Most of coins/tokens hosted ieo on p2pb2b are scams
I wouldn't say that I haven't followed any IEO done on the exchange. Maybe you can post some you know then we look at the project.