Reseller accounts are setup to use one IP address which is
shared between all hosted accounts. This usage is perfectly
fine and there is no reason to host all websites on different IP
addresses. This shared IP address is not intended to be used
for IP access and the domain name should always be used
instead.
The website shown when the IP is accessed directly depends
on the order in which the accounts were setup. In most cases
your main reseller account domain will have been setup first
so this will show when the IP address is accessed directly.