Because showing you know so little about nutrition that you will buy random supplements will avoid people noticing you have only just started attending, are using low weights and focussing on form if intelligent or doing yourself damage if not.
Every trainer is a newbie in the gym at some point, even ‘seasoned’ trainers like me were. This is not to be ashamed of, be proud that you are part of the minority who have the guts to start a lifetime journey into fitness and performance.