Furthermore, leavers may give this as the espoused reason for leaving because :-
a) it's credible - especially as the next role is likely to be paying more.
b) it avoids having a more uncomfortable conversation about the possible "push" drivers that led them to start looking in the first place.
There is also the insidious motive for those in the recruitment industry (and associated fields) to promote salary as a main issue in an attempt to push up their own earnings. (Commission on a higher salary is greater than on a lower one - thereby improving earnings in their own role.)