Do I really need to replace the anode rod?
Most water heater tanks are steel with a thin glass lining to protect
the metal from corrosion. Since the lining eventually cracks, tanks
have a second line of defense against rust: a long metal “anode rod”
that attracts corrosive elements in the water. When the rod itself
becomes so corroded that it can no longer do its job, the tank soon
rusts out, leaks and needs replacement. However, if you replace your
water heater anode rod before it fails, about every five years, you
can double the life of your water heater.
source

The fact that plumbers don't often do this shouldn't be taken as an indicator that it isn't important. The homeowner may not be aware of the purpose of the rod or the resulting benefit from changing it, so they don't ever call the plumber to do it. Few plumbers are going to maintain service records and call you to suggest you have it done.
The guidelines for replacement are averages and your situation may be different. You can either 1) change it on a fixed schedule and hope that's often enough, or 2) change it when you're under the impression that it's not doing its job.
In short, it's up to you.