Once you've gerrymandered yourself into place, what can displace you?
People move. Neighborhoods change. There's an election every two years. For example, some time back Texas had a law where you could only redraw districts every ten years. Texas realized that their safe gerrymandered districts were no longer safe. Passed a law saying they could have a "special" redraw (this is when Tom DeLay was in Congress, before he went to prison). The backlash saw a bunch of Republican districts flip to Democratic control. Not enough to take over power, but enough to scare them from trying that move again.
Texas is inexorably becoming a blue state. There are court cases to compel the state to use an independent commission to draw districts fairly. If those cases are successful, we will learn that Texas has actually been a blue state for a good long time, with the people being held hostage by a hostile government.