I remember watching a draft match for a professional, sponsored team in a moba.
One player taunted during the preface, and after a few kills.
After the match was done, he got chewed out by one of the scouts.
The basic reasoning was because not only was it needlessly disrespectful, but it wasted time and in the case of the pregame needlessly revealed positions.
So for anybody wondering why taunting and the like are seen as a big deal, think about the context as less like an after-work/school activity to blow off steam, and more of a professional sport.
Professional sports you say