If it is meant to describe sexual attractions, and since he is cherrypicking letters he likes in what is actually an unified political movement, and to be facetious, shouldnt it include the most popular sexual attraction type?
The article is literally about bisexual and same sex behavior. So in this case it would not make sense to include heterosexuality, even though that is the most common.
This is not meant to dismiss anyone's identity or experience, just pointing out why gp would "drop the T".