If you have ever noticed the front pads are much thinner than the rears at a brake job, that is completely normal. Front brakes do the majority of the work. Here is why front brakes wear faster than the rears.
Weight shifts forward when you brake
When you press the brake, the car's weight lurches forward onto the front wheels. That extra load lets the front tires and brakes do more of the stopping without locking up - so the braking system is designed to send more clamping force to the front. More work means more wear.
The front usually handles 60-70 percent
On most cars the front brakes provide roughly two-thirds of the stopping power, which is why front rotors are larger and front pads wear out first - see brake proportioning valve, the part that balances front-rear pressure. It is normal to replace fronts once for every one-and-a-half to two rear jobs.
What this means for service
Because they wear at different rates, front and rear can be serviced separately - but within an axle always do both sides; see replace rotors in pairs. Check the fronts more often since they lead. Uneven side-to-side wear on the same axle points to a sticking caliper, not normal front bias.
Keep an eye on the leaders
Inspect front pads regularly and watch wear patterns; see brake pad wear patterns. When they reach the limit, fit quality pads and fresh hardware.