OK, technically, nobody really "needs" more than 3 speeds, for general bike riding. (one speed for climbing, one for cruising on flats, and one for downhill or sprinting) And we have had that for about 100 years. That said, we all find some level of technology that we are comfortable with. Maybe need is a poor choice of words, and instead, I would say, things I would miss if they went away.

I am speaking only for myself, as someone who has ridden everything from old school "10 speeds" with downtube or stem friction shifting, toe clips, old school mechanical speedometers, to a large number of indexed shifting bikes (3 x 7, 3 x 8, 3 x 9. 1 x 8, and most recently 1 x9), the modern things I would miss if they went away are 7, or 8 speed cogs, triple chainrings, indexed shifting, modern bike computers, and clipless pedals. And, there is no way I would ever want to go back to toeclips, heavy steel wheels, downtube shifters, or 5 speed freewheels. I don't own 10 or 11 speed, but I do own 9 speed. If I had to, I could live with 7 or 8 speed, but not 5 or 6.