The simple answer: banks would rather be plundered than fork out cash for beefed-up security.
Employing extra guards and enhancing security technology at branches would cost banks far more than the amount lost to the robbers. In addition, banks are well insured against heists.
Hiring a single security guard costs around 240,000 pesos a year per branch, according to Dante Haro, president of Guadalajara City Hall's Citizens Security Council.
The average haul from each heist last year was 63,000 pesos, according to the Fiscalía General del Estado (Attorney General's Office).
Haro is highly critical of banks that equate security with a bottom line number, thereby potentially placing their customers' lives in harm's way.
Banks in Mexico are governed by federal regulations, which do not oblige them to provide guards in their branches.
Haro would like to see legislation passed at the state level to force banks to take responsibility for their own security.
Several previous agreements between Jalisco authorities and banks that saw state security officers deployed to monitor banks have floundered amid acrimony.
However, as bank robberies began to mount up this year – especially in Guadalajara, where 130 of the 138 robberies were carried out – the Fiscalía General deployed undercover officers in certain parts of the metropolitan area in a bid to catch some of the perpetrators.
According to the Fiscalía General, investigators have successfully resolved 89 of the bank robberies and arrested 43 people. Another 64 suspects are being sought, and nine criminal gangs dedicated to bank theft have been dismantled. The agency made no mention of how much money has been recovered from the total bounty of 8.77 million pesos.
The robbers mostly made off with smaller amounts, generally around 20 to 30,000 pesos per heist. The biggest haul was on April 1, when robbers assaulted a bank at the corner of Americas and Colomos, pocketing 600,000 pesos.
The state of Jalisco is in second place in the number of bank robberies in 2013, behind the State of Mexico with 283, and ahead of Oaxaca with 82.
Perhaps more worrying for the general public is the sharp increase in the number of street assaults on bank customers who have made cash withdrawals from a branch.
The Fiscalía General estimates that criminals in Jalisco stole 18 million pesos from bank customers last year through these kind of crimes, known in Spanish as "asaltos conejeros."
Gang members join lines in banks and are on the lookout to see which customers are withdrawing large sums of money. Once the victims are targeted, they are often followed in their vehicles and assaulted at gunpoint a convenient point, usually a traffic light stop.