= Solution
Two reasons to prefer more advanced methods for smooth, high-accuracy optimization are:
* \b[Slow progress on ill-conditioned problems.] On an elongated quadratic level set, successive negative gradients can zigzag across the narrow valley. Convergence can be only linear with a factor close to one, and line search cannot remove the underlying poor scaling.
* \b[Failure to retain curvature information.] Each new step again uses only the current gradient. <Newton's method> and <quasi-Newton methods> exploit curvature to obtain substantially faster local convergence under suitable hypotheses, often compensating for their more expensive steps.
The question's blanket wording is too strong: the <steepest descent method> and related gradient algorithms are used in practice, especially when problem size, cheap gradients or simplicity make curvature-based alternatives costly. The objections describe limitations, not universal nonuse.
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