In traditional environments wi-fi can provide access to internet connection. However, wi-fi also has its downsides especially in environments that Mercato typically operates. Its stability is dependent on the wi-fi setup in the venues. In addition to wi-fi stability, there are other reasons why Mercato doesn’t use wi-fi. 
Using wi-fi means Mercato can’t fully ensure that the tablet will be up and running as soon as it is plugged in. The host is required to connect the tablet to wi-fi which would significantly increase the operational complexity
Depending on the host to connect to wi-fi means time and risk. The tablets run in kiosk mode and the host can’t easily access the wi-fi menu. Host would be required to perform a new configuration that is time consuming, complex and presents security risks.
From AU experience, additional tasks for the host result in negative user experience and poor compliance. If additional tasks are to be executed by the host, compliance will take a big hit making the execution counter productive 
Wi-fi signal and stability, like 4G, is dependent on where the tablet is located. So, even when a tablet is connected to wi-fi, there is no guarantee the tablet will have consistent and quality connectivity as varying loads to the wi-fi can alter this at any time.
The internet provided over wi-fi is as good as the plan that the venue is subscribed to. The venue owners might be subscribed to a slow plan. Even when the internet plan provides fast internet, many wi-fi systems used in venues are shared with guests, compromising the stability of the network and often making it unreliable. 
Depending on the wi-fi setup and the access points, wi-fi can randomly disconnect and not connect again automatically. When this happens, the host will have to re-connect manually going through a new configuration.
Internet provided to venues is not always through hard wired cables. Many internet providers facilitate internet through the use of 4G modems. In areas with poor reception connectivity can be very compromised.
Many wi-fi networks sit behind firewalls, adding a risk that key functionalities of the system may fail as a result of outbound and inbound requests being blocked. Therefore, for hosts with firewall protection, all requests from the Mercato system would need to be whitelisted. At scale this could become extremely time consuming and administratively difficult to control.
Many venues have unprotected wi-fi presenting a major security risk despite the Mercato system being very secure all communication is encrypted.
Although Mercato works with any internet connection, using wi-fi will result in significant operational difficulties and security challenges. As observed in AU, not putting tablets in certain areas is not ideal where 4G range is poor, but it is preferable to have high quality and high compliance vs low compliance and increased operational complexity.