Chossid, it is a minhag like all minhagim. It was originated at a time when Bitul Torah was precious and even if its not anymore as it once was, the minhag stayed on. Same way chassidim daven late because once upon a time, chassidim in Peshischa and Kotzk purified their minds and souls many hours for davening, starting from the early hours, which is totally not relevant today…
