Know more about EU set up but the reality is that there is a lot of infrastructure costs and some fraud as well (~4.04bsp @$101 average). So costs for ~$2000 in fees can be up to ~$400. Signature cards are not secure whereas EMV cards hit a 0.42bsp fraud rate ($148 average).

Of course still room for profit but the above numbers show why merchants are interested in EU fees and security.