It is a fact that there are more female JWs than males. This results in the problem with the problem that there will be single, unmarried females with no prospect of finding a partner. Naturally the prettier females will be cherry picked.
There is occassionly talks and literature trying to address this problem of singleness.
Herds talk is aimed at putting it in the minds of single sisters that even if they are not pretty there is still a chance that they will be selected as a potential marriage mate. They must work hard on their inner beauty.
Its another form of control in the guise of giving hope to unmarriageable mates.
To some extent, he is also telling males to consider marrying Sisters who show dedicated JW qualities. The thing is, most males can, for the most part, have both and if you are a Bethelite, you get to pick young females as well.
It hasn't swayed GB Mark Sanderson in any way.