Wind power is often described as relying on "mature technology" and, in many contexts, that's correct. Today, well-sited wind farms in the US and EU generate electricity at a lower cost than coal.
But there remain numerous difficulties with the way we build wind turbines, which raise the price of the turbines, which in turn determines where they can profitably go. High turbine costs mean that, unless the wind at a site is quite strong, there are typically better ways to spend money.
Fortunately, while wind is mature technology, it hasn't reached an evolutionary dead end. Plenty of incremental changes can make wind even more affordable—and in many cases, the necessary technology is already being tested.