It's not that simple. First of all, the goal is to track the index as closely as possible, not to get the best price and certainly not to avoid illiquid stocks.

It's not that simple. First of all, the goal is to track the index as closely as possible, not to get the best price and certainly not to avoid illiquid stocks. Moreover, how would you balance these two algorithms' holdings? Regardless, there are a great many nuances, complications, and technicalities involved in trying to keep an index fund on-target. Not just the pricing and liquidity issues mentioned in this article. This is especially true for very large funds with hundreds of billions under management. Index funds are as close as one can get to full automation today, but taking the last step to full automation won't happen without fundamental changes in underlying systems like the exchanges. It's not clear if it would even be advantageous to automate human decisions away completely here. Proposed automations often run in parallel simulations to a manager's work and are plugged in when they seem empirically to do better than a human manager can. Obviously that hasn't been the case across the board just yet.