There are many individuals of the few species found in these forests. Wind pollination can work in angiosperms too, where almost-monocultures occur. An example are the grasslands and savannahs. Here huge stands of a relatively small number of species occur. There is plenty of opportunity for stigmas to be down-wind from anthers.
Most grasses are wind-pollinated.
Angiosperms that live in, say, a tropical rain forest cannot use wind pollination effectively. In the surrounding acre, there may be several hundred different species present. The next individual of a particular species may be quite some distance away and at some unknown angle with respect to wind direction. The plants of one species are few and far between. Animal vectors are smart enough and agile enough to do this.