I can think of a couple of possible explanations for this:
1 - The large number of people who had COVID-19 and suffered organ damage made them more susceptible to hospitalization from the flu.
2 - The increased surveillance for COVID-19 and the need to differentiate the two diseases has lead to finding more case of flu.
3 - Possibly a more virulent strain of flu this season. About 3/4 of cases from recent surveillance are N3N2, which historically causes more serious illness.
The source to the previous figure is #cdc. https://www.cdc.gov/flu/weekly/index.htm