The tradition of putting blockbuster IPOs on Saturdays was to drive traffic to HSX on the weekends where is was usually dead (because of weekend opening moviestocks halting on Friday to Sunday).
HSX ended commission free Saturdays in Sept 2009 (RIP The Horn Of Gondor) for two reasons... it was originally offered to help players who played during the week with a fast interent connection at work but had to access HSX from home on the weekends with a slower internet connection (remember dial up?). Home internet connections got better over time and commission free Saturdays became very popular and it ended up that commission free Saturdays almost became like coordinated trading with blockbusters (highest priced stocks and most widely held stocks) being massively traded for profit and drastically affecting price and volume with damaging results for the game.
https://www.hsx.com/forum/forum.php?id=3&pid=15499
"The incentive was originally created in the late 90's to encourage trading on the weekends, a historically slower period of trading activity when people were at home and dealing with the inconvenience of dial-up. Obviously, those days are long past.
A study performed by HSX Staff showed conclusive evidence of a number of anomalies that were discovered during the commission-free period. In short, we concluded that HSX Traders were responding enthusiastically to the incentive, but also, in effect, warping market activity.
We believe that by removing commission-free trading we will reduce gaming of the Exchange and encourage a more natural market. And while we cherish those devoted souls who were willing to spend their weekends re-shorting their portfolios, We hope that our Traders will instead concentrate their efforts on making judgments on the price of securities."