Well, there is something that we as humans tend to ignore: a lot of benefits that come along with employment. Having spent around 9 years now in the industry, I am sure it has to do with the individual culture and, more so, the perception of the candidates when it comes to making a choice between comparable baseline packages with different benefits and incentives.
The perception arises from a "Not sure" thinking on the part of candidates as to whether they would actually be earning the benefits or if it is merely an eyewash to project a better package. This holds true for the incentive-based benefit component in the compensation package. Additionally, if a candidate is certain that he would be earning an amount X slightly higher than another amount Y, even though the latter offer includes many other benefits, the candidate chooses the former. This is because at the end of the month, people definitely evaluate everything in monetary terms - i.e., how much money is transferred to their Salary Accounts.
Thanks!