A lack of an exodus does not indicate a lack of new interest. Now instead of investing in France, for example, some investors may invest elsewhere. Football stars may play for other teams, and celebrities may decline French endorsement deals. Corporations in France pay all of those people high salaries because of their value on the international labor market for their respective positions. By effectively reducing that rate, France forces those corporations to either increase salary significantly or lose some future prospects. Football teams, large corporations, and brands may all decline to raise salaries, and thereby France may see a reduction in culture (brands, football) and FDI (loss of foreign interest in investment).
This is personal income tax, for physical people living in the country. Investors don't need to take actual residence in France to invest in this or that company, so that's not really going to change anything. Any celebrity worth that money is already living in Monaco (or similar tax haven). The only people affected by this are millionaires who, for some specific reason, are forced to live in France: footballers and very few others. Hence why revenue projections are actually quite low.
