This sort of experience is probably better termed a heuristic rather than a bias. The two can be related in some cases (as heuristics can cause bias when the underlying model does not fit the real situation).
From the Wikipedia page linked above, a heuristic is:
any approach to problem solving or self-discovery that employs a practical method that is not guaranteed to be optimal, perfect or rational, but which is nevertheless sufficient for reaching an immediate, short-term goal
Choosing to manipulate the easiest variables to manipulate first is an example this. It is practical, but may not be optimal. Since there is a low cost to manipulating the easiest variables, you might save some time and effort if one of those manipulations does happen to work, even if it was improbable. Not only do you avoid trying to more complex solutions, but you also avoid expending the mental effort of determining which one to invest in trying.
A well-known and often-lamented example of this sort of heuristic is in tech support decision trees that often start with steps like "Is the power on?" and "Have you tried turning it on and off again?" These steps seem a bit silly, and often have nothing to do with the symptoms of the problem, but if they happen to work it saves the support representative a lot of further time and effort investigating the problem.
Of course, this heuristic will fail if you manipulate a lot of "easy" variables - in that case, the sum time to try all the easy steps might be more effort than it would have taken to use some mental effort in the first place.