A. Unlike the Wildflower Inn, Martin's Cafe serves considerably more meals on weekends than it does on weekdays. -- This does on give information pertaining as to why Wildflower Inn's now servers more meals on all days . Nor is the time line given, for all we know , WI has always been serving more meals on weekends.
B. Most customers of Martin's Cafe had never dined in Riverville before this restaurant opened, and on most days Martin's Cafe attracts more customers than it can seat. -- Can be a possible explanation for why WI now servers more meals .
C. The profit per meal is higher, on average, for meals served at Martin's Cafe than for those served at the Wildflower Inn. -- Banal . Nowhere does the author talk of profits .
D. The Wildflower Inn is not open on Sundays, and hence Riverville residents who choose to dine out then must either eat at Martin's Cafe or to neighboring towns to eat. -- Would weaken the argument.
E. A significant proportion of the staff at Martin's Cafe are people who formerly worked at the Wildflower Inn and were hired away by the owner of Martin's Café -- Banal.
Hence the best answer would be B.