Yoga is Often Commingled with Religion
There is an old saying that, "If it looks like a duck, and it walks like a duck, and it quacks like a duck, then it must be a duck!"
This is where the problem arises with Yoga and religion. Sometimes, when one encounters Yoga in particular organizations or groups of people, it can look very much like a religion. This is because some of the teachers and practitioners of Yoga commingle Yoga with religious practices. This is particularly true in the arena of Bhakti Yoga, the Yoga of devotion. From the standpoint of Bhakti Yoga, it is the devotion that is the point, not that a particular object is suggested for that devotion. Thus, one may practice Bhakti, or devotion, from within his or her own religious preference.
When the teachers practice their own religion in the context of Yoga, and present that to their students, the students end up with a mixture of Yoga and religion. The student may know the theory (and truth) that Yoga is not a religion, while at the same time those same students are practicing the religion of their teacher in addition to practicing Yoga.
Gradually, Yoga and the religious practices blend, and suddenly you have a religious duck named Yoga! This does not mean that Yoga or Yoga meditation is a religion. It does mean that a particular organization, lineage, or system may have taken on the coloring of religion, and within that sphere, there is religion being practiced.

...what the obsession with Yoga and Religion is!
The concept of "Religion" clearly defines itself : the service and worship of God or the supernatural, personal commitment or devotion to religious faith or observance.
None of this is in Yoga!