Question

Why do some plants bear long anthers?​

Answer 1

This types of plants are $\color{red}{wind pollinated}$

So there pollen grains can be easily flown off by wing for further pollination...

Eg_Maize

Answer 2

The main reason is the genetic behaviour in different plants.

Pollination is the act of transferring pollen grains from the male anther of a flower to the female stigma. The goal of every living organism, including plants, is to create offspring for the next generation. One of the ways that plants can produce offspring is by making seeds. Seeds contain the genetic information to produce a new plant.

Seeds can only be produced when pollen is transferred between flowers of the same species. A species is defined a population of individuals capable of interbreeding freely with one another but because of geographic, reproductive, or other barriers, they do not interbreed with members of other species.