If the exchange has good credibility then they will be more selective in accepting a project entering their exchange.
In crypto world we must be smart and must always be willing to carry out our own research on what project are good, not just based on where the coins/tokens are listing.
That's why when they want to be listed on big exchange they need to wait longer because if this scam project will be listed on their exchange it will affect their reputation. they will end up getting some negative feedback from their community.
As you can see, you need to wait for long to get your coins listed in Binance exchange even some legit project will need to go to this procedure.
and in some other exchanges needs to have the community decides if the coins or tokens will be lists on their exchange. by making users vote for those coins or tokens.