That's basically how NetWorx was designed. It runs as a regular application when a user logs on. Otherwise it does not run, i.e. it is not a service.
If you are looking for monitoring server bandwidth, a different product called Bandwidth Manager may be more suitable. It runs as a service, allows you to define a variety of monitoring rules, and if necessary configure bandwidth caps and quotas.
It is worth noting though that this product can handle about 500 Mbps at most.