Why do Brahmins still perform Upanayanam

Why do Brahmins still perform Upanayanam (sacred thread ceremony) when most of them who undergo that ceremony don't follow the practices that they are supposed to? I will explain this as a Brahmin and who has undergone Upanayana a long time ago(>5 years). One thing you need to know is that in most Brahmin homes, we are taught never to eat non- veg. Some people do do that when they get older and it is their personal choice. For me, the main difference of undergoing Upanayana is the 'Sandhyavandana'. I practiced it twice a day for a year(we are supposed to do it thrice a day) and found myself concentrating far better than I used to and yes, I was way more calmer. Even now, whenever I do Sandhyavandana (the longer version with pranayama and all) at least once-a-day for a week, I grasp information better and do not feel stressful at all. And yes, many of my friends have experienced this too. So, to sum it up, Upanayana leads to Sadhyavandana which is beneficial, to say the least!