Miriam Shaviv has an excellent post on the customs of Simkhat Torah based on Avraham Ya'ari's classic history of the festival, 'Toldot Chag Simchat Torah' ('The Origins of the Festival of Simchat Torah,' pub. in Hebrew by Mossad Harav Kook):
The festival originally did not involve reading from Bereshit, but merely finishing Devarim. Hence, the original term was not 'chatan Torah' but 'chatam Torah' -- sealer of the Torah. There was, of course, no chatan Bereshit.
The original name wasn't 'Simchat Torah' but 'Yom Habrachah' -- the day of the blessing, after Vezot Habrachah -- the last chapter of the bible which was read on that day, and after the haftarah they read then, in which Shlomo gave blessings (I Kings 8:22).…
But, perhaps most importantly:
The minhag of hakafot is an adaptation of the minghag of going round the bimah seven times on Hoshanah Rabah with lulavim/aravot. Hakafot on ST were not known at all until the last third of the sixteenth century, and the first time we hear about it is in Tzfat in the days of the Ari, from where it spread out to other communities. Previously, some communities in Ashkenaz took out all the Sifrei Torah, but it took 150 years for the minhag of hakafot to spread, after it was mentioned in several books and after Jews from EY travelling to other communities helped institute it.
In other words, the minhag whose purity Rabbi Hershal Schachter is fighting so hard to retain was not commonly practiced until it was spread during the messianic fervor surrounding the false messiah Shabbatai Tsvi. [Note that Ya'ari fails to mention the remarkable "coincidence" of the custom's spread and Shabbatai Tsvi's heresy.] This may also account for the more rowdy customs and the treatment of this holiday – which was originally a siyyum – as another Purim, complete with much public drunkenness and frivolity, two things that marked many Shabbatian (and later Frankist) -inspired events.