I agree with you IF we are regarding Mr. Bennett as a realistic character -- but I don't see him that way. I see him (so far in the book) as a stock figure out of older comic traditions. For me, a stock character doesn't need "motivations" and can't be held to the same ethical/moral standards as more realistic/3-dimensional characters. He rolls his eyes at his wife and daughters instead of trying to direct or influence them because that's what his literary type does. Not because he's a lazy or irresponsible person.

I think one of the interesting things about Austen is that she is on the cusp between a comic and a more serious or "psychological" way of understanding and depicting character. For some of her characters (like Mr. Collins), she at least sketches psychological explanations for their behavior. (An earlier post noted Mr. Collins' tyrannical father as the source of an insecurity which Mr. C shows in his toadying and boasting. Similarly JA explains Lydia's flightiness and pushiness as the result of her mother's over-indulgence.)

Others are more stock comic types whose psychology Austen doesn't explain; I would put Mr and Mrs Bennett in this category: the philosopher and the "very silly woman."