The frequently cited "70 word attention span" is, at least as told to me, a number derived from research on the effectiveness of advertising. As advertising is needed only when you're trying to sell your product in preference to another when there is no difference between the products it may be taken to be the limit for the average ¹idiot (which unfortunately has far too many synonyms among general populations.)

The above 70 words likely will be incomprehensible to anyone to whom the 70 word recommendation is really applicable, which quite fortunately includes only a few regular 'catters (?).

¹ COFs may use "anyone under 30 (or 40) or... " as a synonym in many situations.

John