fields of linguistics
Linguistics itself encompasses many different fields of study. Many linguists specialize in one field of linguistics. Some fields of linguistics are older than others, and some are relatively new. Some fields are even disputed as "fields" within linguistics at all.
Phonology and Syntax are two of the oldest fields of linguistics and they both have the most history and research associated with them. It is fairly easy for newcomers to linguistics to come into Phonology and Syntax studies because of this.
The fact that these two fields are older and more well-researched is because of the history of linguistics itself and the development of the two main branches of linguistics, Generative vs Cognitive Linguistics. Because Generative Linguistics came first (around the 1950s) and is highly associated with Phonology and Syntax (as well as Morphology), these two fields of linguistics have much more research associated with them.
The newer linguistic fields include Sociolinguistics, Gesture Studies, and the ongoing debate about Semantics, each of which you can read about in their individual pages. These pages are merely introductions and by no means contain all of the information there is to offer about each field.