Real-Brisker –
If I had to hasten a guess it’s due to the different types of yarmulkes worn in the different circles. When I first became frum I was wearing a suede yarmulke and had trouble keeping it on my head so it necessitated a clip/pin. As I grew in my Yiddishkeit and Avoda and began to associate with the Yeshivish community, I upgraded (tongue-in-cheek) to a felt yarmulke. Due to the size, material, etc. this yarmulke keeps on my head without a clip/pin. In conclusion, the respective yarmulke style in each community either necessitates or does not necessitate a clip. Kol tuv.