Because wind power is intermittent and highly variable, it requires either back-up power or battery storage to be useful, i.e., steady and available when actually needed. This is a simple fact of off-grid living, for example, which requires a large bank of batteries and usually a diesel-fired generator as well.
Just as wind power itself is practical only on a small scale in places where its expense (which is due to the energy source being so diffuse) can be justified, because other sources would be equally or even more expensive, so is the required back-up and battery storage, both of which add not only to the expense, but also to the environmental impacts of wind energy.
On the electrical grid, just as for an off-grid home, wind energy can not stand alone.
And the need for back-up sources to supply power for more than the short time (a few minutes to an hour or so) that batteries might provide underscores that wind energy is, in the end, a superfluous add-on only, a mere symbol – one that is not only expensive and harmful, but also virtually useless on a large scale.