1). Because, you risk to see a more complete extension of your invention, quickly published by academics who have a faster access in scientific journals or patented by third parties, with a priority date that is before your application date.
2). Because, you risk to finally be rejected by scientific journals of high impact factor that generally demand a lot of supplementary work, take a long judgment time and they are very strict to not well-known researchers that come from the middle of nowhere. Besides and in real life, the most of them historically were not and they are not friendly to “real” novelties.
3). Besides, open access publications are more often read, downloaded and cited.
4). As far as I understand, what you need is ensuring your intellectual and/or industrial rights, before getting in contact with third parties that might put your invention “in the refrigerator”, in order to exploit it later.
PS: The number on secrecy months may be different in different countries. So, look at your country Patent Office, as punctually AWK remarks.