If you contest a ticket and the officer does not show up you win a default judgement. Perhaps they are playing on the fact that unless they are on duty on the scheduled date, they are probably not showing up at court.
Many jurisdictions will pay officers to appear and many don't factor appearing into their budgets/schedules, so the officers are paid at overtime rates (time and a half). Many officer's don't mind having to appear... they make bank and many pensions are based on the three years of highest revenue (this is a method officers abuse in Wisconsin... they will work as much OT as they can for three years especially near retirement, since the legislature hasn't bothered fixing/forcing pensions to be based on 40 hours / week.)
Mirroring what jrs235 said, I've also heard officers schedule court appearances all together so it's more convenient for them to show up.
I doubt it makes financial sense for them to do anything at all past an initial letter contesting the ticket. If they get it dismissed, they make 25%. Otherwise they walk away and say "sorry, we tried."