less chumros
Part of the answer to your question lies in the fact that the kriah for Simchas Torah (i.e. the second day of shemini atzeres even before it recieved the name “simchas torah”) is Vezos habracha. This has nothing to do with regular Shabbos reading
Even when the Torha was finished in three years. On Simchas Torah they lained vezos habracha. See Gemara end of Megila. Rashi gives the reason based on birchas hamelech
With time this turned into the Simchas Torah we have today