I think in the case of an eligible single man who might want a family of his own, the first thought would not be to have him matched up with a widow but instead with a woman who might give him children of his own.

If he had been previously married--say at 23 or 24, and lost his wife and was left with some children around 9 or 10 years old, then Mrs. Dashwood might seem to be an equal or even more eligible choice than her daughters.