It is just technology. Model T's were two speed, new cars are six with overdrive.

You get more out with less in. Matches up the motor with the chassis.

I have two bikes, one is 7/3 the other is 8/3, both cassettes. The big
difference is the 8 has an 11t and the 7 a 13t. the chaining and the
large cassette cog are the same on both bikes. The 7 sp bike has
slightly smaller tires and runs in one gear higher most of the time in
the same situation. It is also a bit lighter, couple pounds.