It’s not the one, true, church. That’s all.
Well, more to the point, many Protestant (and Evangelical) ecclesial communities (not Churches) have a structure in place where it is permitted for the
hoi polloi to invent and dictate liturgical innovations. In these ecclesial communities there is a cacophony, a Babel, of praxis, not to mention doctrine, that reflects the anarchic and decentralized structures of, what, 30,000 denominations?
Whereas the Catholic Church is one, holy, and apostolic. We have one hierarchy and one Vicar of Christ. Liturgical innovations are either deemed organic and codified, or frowned upon and reprobated, according to their appropriateness. Our liturgical books are regulated centrally and promulgated universally so that we may have unity of worship throughout the world.
Now, I don’t know which way the Church will come down on hand gestures such as this. It has really never regulated gestures to a great extent. In all probability, she will never rule on something so trivial as this. For the foreseeable future, this remains a personal preference, and one which I do not prefer. I personally mimic the altar servers, who stand reverently with hands joined in front of them. I adopt this posture unless I am holding something, like a hymnal, which in the choir, I often am doing.
The half-orans and orans postures are very low on my list of things that annoy me about liturgy. They are a personal choice, unregulated by the current books. I feel that if I just leave those people alone, the custom may die out soon, due to the post-Vatican II Biological Solution working its magic. If it were important or useful, then it would be catching on and becoming more popular, rather than less.