There are multiple ways that have been proposed. There’s no reason to keep doing it this way other than to benefit the party in power. And while Democrats have been guilty of gerrymandering in the past, there is evidence that the Republicans played a long game to dominate state legislatures precisely in order to redraw districts and dominate elections.
North Carolina is a particularly horrific example, and have managed to stall implementing a better districting plan despite being slapped down by the Supreme Court. Besides the massive racial and political imbalance in voting, it has led to a GOP-dominated legislature that can ignore constituents entirely, and have taken actions like slashing funding for the once-excellent state schools, and endangering coastal communities by denying scientists the ability to record rising sea levels.