The reason these are considered secret is that they are not beginning level practices. Those outside of yoga practice and those just begining will not have the advanced awareness to understand the purpose and method of these sorts of practices. They may judge these practices negatively because of their external appearance, and they may intimidate or disuede them from practicing yoga at all.
Part of the secret yoga practices, the 'inner work' is the process of slowly expanding one's consciousness to heal all wounds, let go of all attachments and understand the nature of being through experience.
The inner work is crucial for our growth spiritually. Although it makes us want to share, the inner work should mostly remain private. That way feelings aren't hurt, and drastic actions aren't taken prematurely. Much of the inner work reveals distractions, distortions and false-views very slowly so to share or act too impulsively can cause harm when the whole realization is reached.
The journey to enlightenment includes a learning from where we have been, learning to overcome temptations and to sympathize with all beings. On the way we learn how others are a reflection of ourselves and we see how we can be everything we had ever judged. We come face to face with the ego, with the obsessive natural of mind, with the chronic dissatisfaction that poses as our inner guide but is just egoic craving.
To share these deep, personal experiences with others would cause more trouble then its worth, because our awareness and experiences on the path are what provide us with insight into the nature of these experiences. Generally, our friends and family aren't likely to be able to give us the feedback we could use for growth. Brothers and sisters on the path may be able to, and certainly our guru or teacher can.
Dragging raw, unfinished experiences into the language of expression can betray the real depth and internal value. Being patient, non-judgemental and just watching the experience over time will eventually tie up all loose ends, provide understanding and leave a feeling of completion where the nagging questioning once was.
We can trust our experience and our intuition to tell us whether to share or let the lesson happen internally.