That sounds like usual risk aversion. How is that a bias?

Loss aversion is different than risk aversion, though they are related concepts, the shape of an agent's utility function under loss aversion can lead to inconsistent preferences.

Why in recent years? Why aren't these funds more common? And since you are talking about "rebalancing" in the next >paragraph, are these funds really automatic, like index funds, or do they still require active portfolio managment?

I can only speculate as to what the average of all the millions of decisions that go into releasing an investment product and whether it gains popularity looks like. As to why in recent years, I think it mostly is a function of the rise of index strategies, the emergence of the ETF as a vehicle that is well-equipped to execute strategies like this, and the general fall in popularity of expensive, black-box, active management strategies.

Internally, these products rebalance according to some rules-based methodology. IMO the "active vs. passive" debate is a false dichotomy, the better scales to judge an investment by are "cheap" vs. "expensive" and "transparent/rules based" vs. "black box/dependent on skill." Some of the enhanced index funds are in fact cheaper than some of the "true" index funds on the market.

Externally, there is currently no such thing as target date retirement fund which tries to strategically target these factor premiums in a rules-based fashion, they are generally limited to single-asset classes and so will require some measure of asset allocation/portfolio management decision making.

I think there is a kind of "meta" risk you are not considering here: index funds are proven investment strategies, based >on empirical evidence and economic theory. The investment strategies you propose here are more uncertain. You link many studies in favor, but I don't have the expertise to evaluate their relevance, and I suppose this holds true >for pretty much anybody who isn't a professional investor. From the "outside view", the strategies you propose are inherently more risky than index fund investment.

I basically agree. And you may say the possible greater expected return from these strategies is compensation for this meta-risk. As I am quick to point out, these strategies do underperform from time to time, sometimes badly. It is during these periods that investors proclaim that "things are different now" and change course, often to their detriment. This epistemic factor can make the strategies more risky in practice.

I have laid out what I consider to be the best evidence to support my philosophy, much of it is Nobel-prize winning research (not that having Nobel laureates on your side is always profitable...) But how comfortable you feel evaluating that evidence or trusting me to present it in a fair manner is a question I can't answer for you. If you are doubtful, and I do not find that an unreasonable proposition, you would do well to use index funds and be done with it. More intrepid investors may have a different attitude.