A constant rise in the number of scientific journals has been recognized for a long time. Presumably, Derek J. de Solla Price was the first to quantitatively analyse this trend, see his book "Science Since Babylon",  published 1961 (Yale University Press). Factors like increasing pressure to "publish or perish" might contribute, but the rising number of journals is a general phenomenon, and for various disciplines, not only health sciences.

Dear Shyam,

You ask for the reason why there is a rising number of Health Sciences Journals in the world. Note that this rising has occurred in every scientific domain. I see several reasons for this to be case. (1) the widespread "publish or perish" policy followed in many countries all over the world, namely in the United Stages of America. As it seems obvious, this policy leads to the rising of scientific papers almost all over the world, and hence, of scientific Journals. (2) With the passage of time, we generally know better and better of the unknown in any domain of reality and, hence, it is likely that there are now more scientific papers than it was the case even in a relatively recent past. Again, the increase of papers generally means the increase of Journals . (3) Note also, as the critic John Horgan (1991) once remarked, that theories of human nature never really die; they go in and out of fashion. More theories also mean more scientific papers and Journals. Last, but not the least, to have a healthy life is a widespread desire and aspiration among people. This desire has led to a multitude of, say, medical specializations. This generally means an increase of findings to be shared and published in specialized Journals.

A caveat is now in order. The increase of scientific Journals in a given area of knowledge is not always a token of scientific progress. This is particularly true in the so called "soft sciences". Suffice it to say that in these sciences several findings and theories result more from, say, artificial than natural fractures. For example, in developmental psychology, which is my area of expertise, we have countless theories, such as Piagetian theories, neo-Piagetian theories, post-Piagetian theories, anti-Piagetian theories, and neo-neo- Piagetian theories. We might even say that if the number of theories were a critical criterion for scientific progress, then psychology would probably be the queen of sciences, which is not the case.

Needless to say, my answer to your question is a short answer. Even so, I hope that it provides you with some hints as far as your question is concerned.

Best regards, Orlando