Up to the 1990s, and maybe later too, when you bought a floorstanding speaker cabinet there most likely be a tweeter, a midrange, and a bass driver. Now you will typically get a tweeter and two identical lower frequency drivers. Why did that happen and over what period did the switch occur? I suppose there was technological improvement that meant a 160mm driver could now handle midrange and bass sounds with good balance, and that was not possible earlier.
Now, when I write 'typical', I mean most floorstanding speakers costing up to £1000 roughly. I know there are many setups that employ 3 different drivers but I don't think these are typical any longer.