Temporary restrictions on betting against stocks have been extended in Europe, even as investors bemoan the problems such bans pose and their lack of effectiveness.

France will keep the curbs on short-selling trades in place until May 18 because of “a serious threat to market confidence,” its markets regulator said Wednesday. The CAC 40 benchmark of French stocks has lost roughly 27% of its value since the start of the year, even as the S&P 500 pared back declines to about 14%.