Why? The name of the current rule has no effect on the value of this built-in variable.
Have you read the docs yet? While RM is a complicated app (and not the first one I'd suggest for most automations), many questions like this one can be easily answered by looking through them. Here are some previous suggestions:
From https://community.hubitat.com/t/please-help-with-rule-logic/155794/12:
From https://community.hubitat.com/t/how-to-set-a-variable-in-the-trigger/155820/8:
From https://community.hubitat.com/t/how-to-set-a-variable-in-the-trigger/155820/31:
As for this particular request, @marktheknife's explanation above is undoubtedly the case. From https://docs2.hubitat.com/en/apps/rule-machine/rule-5-1#local-variables-1:
%device%: name of the device that generated the most recent matching trigger event
So, this just means that was the last trigger event that fired your rule. It has nothing to do with your current trigger list per se (aside from the fact that, apart from drastic rule changes, one of them is likely to have done this in the past).
(Also, while you may not have been asking about this specifically, note that your rule is going to send you a notification for all matching devices when any device triggers the rule, not just the notification for the one that triggered the rule -- as currently written, at least, perhaps why you were wondering about this.)