ELI5: Why don't "average return" numbers take *average holding period* into account?

Hear me out because I think many people do not consider this.

1. Many people will withdraw their investments when they *have to*, not when the market is particularly suitable for withdrawal.
2. This means that the market's average annual returns over the past 50 years don't mean that much if it just so happens that you have to withdraw during a market downturn.
3. This means the "average return" you are likely interested in is not "average return till now" - it's the average of "return till X period, return till 2X period, return till 3X period, ... return till now".

This is a relatively different number from the "average return till now" number - depending on how you pick the "X period". This "X period" dictates your actual risk appetite IMO. For someone who feels they might have to withdraw on a day's notice (X = 1 day), the actual average return is a lot lower. Even with 1 month's notice it comes to around 7% per my calculations, not the standard 12% annual returns people assume.

Now I understand there is also a large number of people investing for whom this is not strictly relevant because they have a decent emergency corpus. But nowadays many people are investing without that cover in place.

The closest industry term I can find is "AHPR" (average holding period return) but it's not quite the same it seems? And also not that widely discussed.

IMO it's unfair to the normal middle class investors that this is not clearly communicated to them.

Thoughts?