Why do I have to push my shift lock in order to move my car?

The purpose of the shift lock is to ensure that you have your foot on the brake pedal when you move the gearshift out of park. If the switch on your brake pedal fails then the only other alternative to move the gearshift is the shift lock override mechanism provided for just such an emergency.

If you're tired of using the override, then the thing to do is to figure out what's wrong with the brake pedal switch and fix it.

On some cars it's combined with the brake light switch and on others its separate, so you'll have to see a wiring diagram to figure out which one you have.