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Ticket quotas are a reality. This officer was probably one short, and it was getting close to time to go home.

Ticket revenues usually support the municipalities general budget (more "discretionary" spending by our politicians). The police chief is an appointed position, who serves under the direction of the mayor, who is the main spender of these funds, to repay political debts or whatever he sees fit.
State patrol officers are theoretically more independent, but still have budgetary pressures. Interestingly, in many areas of the South, a large percentage of ticket revenues are directed by state law into an officers retirement fund.

Red-light cameras are always marketed to the municipalities on the basis of revenue increases, with potential enhanced safety postulated but seemingly never supported by data. These cameras are almost always contracted out to vendors providing the service, whose reimbursement is contingent on the revenue received. 2 of the 3 companies offering this service locally were found to have engaged in dubious practices, such as altering the timing of lights and advancing camera timing relative to lights, to catch more motorists.
I won't go into why this is wrong on an ethical, governance, or philosophical basis. If you do not posit that it is wrong for a government to outsource enforcement of the law, or profit from defining its citizens as criminals, then we will have a hard time having an intelligent dialogue.

LEO's are always tasked with using discretion in enforcing the law. They must prioritize. For example, a poorly maintained and fully loaded log truck driven by a logger with a CDL, going 55 in a 45 zone on a mountain road in the rain with poor visibility , probably deserves a ticket. An alert and attentive driver of a well-found sports car enjoying a sunny drive at the same speed & location, probably does not, even though the same law is violated to the same degree.
And if the police stopped every car in Atlanta going 10+, there would be no traffic whatsoever on the perimeter.
So while the idea of "selective enforcement" is anathema to some, it is a reality that lets our society function.
So maybe this officer had poor judgment. But more likely, his judgment was removed from the equation or his priorities shifted by external forces (such as pressure from his shift commander, who himself got heat from upstairs.), or perhaps more personal issues.

But yes, you are right that he clearly was not primarily serving the interest of public safety, or he would have been seeking a larger threat. Sorry you got caught. On the whole, these guys do a hell of a job for not too much money, and many are true heroes. A few are true duds, just like in any field. I try to give them the benefit of doubt.

I once had an officer pull me over for speeding in Atlanta. I was speeding, but I was slower than most cars, and had just been passed by a large group going about 20 mph faster than me. I asked him why he pulled me over rather than one of them. He said "you were easier to catch." I told him "thanks, I'll make sure THAT never happens again!"

My bias: old enough to have seen how the world works, both of my brothers in law enforcement, no recent tickets but one recent warning - was kinda funny, for another day.