F1 is cool. There's Formula 1, 2, 3, and 4 racing, but no Formula 5. Why not?

I feel like it should be

F1
F2
F3
F4
F5

Only F's 1-3 are Global whereas 4 is separate individual championships

F5 could be used as a rebranded Karting Championship then F4 should be one Global championship with the Driver's Champion getting a seat in F3.