I think cheap rare earth magnets was a factor, although I suspect only a part of the reason. The motors are now far smaller, lighter and more powerful, as well

I think cheap rare earth magnets was a factor, although I suspect only a part of the reason. The motors are now far smaller, lighter and more powerful, as well as cheap to produce. Given you need four of them, they are now light enough that a small (therefore also cheap) battery can give a useful range to them, so you can have a very effective device at mass-market prices.