By 1941, Groucho didn't want to make any more movies. The Brothers continued to do so just to keep oldest Brother Chico afloat, due to his gambling habits.
Someone commented earlier about Virginia O'Brien, the deadpan singer in the "rockabye" sequence. The deadpan delivery was her "shtick", and predated a similar approach taken by Keely Smith some years later. Legend has it that the first time a spotlight fell on Ms. O'Brien for an on-stage solo, she froze, an delivered her song with a pre-Botox facial paralysis. The audience thought it was part of the act and roared approvingly with laughter. From then on, Ms. O'Brien sang no other way. (She also sings a few bars of the Jerome Kern song, "A Fine Romance" in the semi-bio, "'Til The Clouds Roll By".) The big store is best remembered (and viewed) for the rousing "Sing While You Sell" piece about 38 minutes into the movie.