That’s a bit like saying why do we need 10, 11, 12 gears for our bikes.
I play quite a lot, for a typical round I would take my 3 wood, 5 wood, 4 hybrid, irons are 5, 6, 7, 8, 9, Gap Wedge/Pitching Wedge and Sand wedge (plus putter)…I have all different loft wedges so these vary…and I have a putter. Certain courses I’ll take a driver and maybe a different rescue / hybrid club…(if it’s a tight woodland course I generally leave the driver at home!)
Typically I know how far each club will travel if I hit it well. So if I’m 130 yards from the green, flag is 15 back, then I know what club I should use (roughly).
No where near as expensive as cycling can be. My clubs are a total of about £2k’s worth and they are considered pretty good clubs. You can buy a starter full set new for about £600.