I think it is unhelpfully reductive to say that the reason for using no crossover, or a minimal crossover, is simply cost. Crossovers cannot add anything to a speaker system - all they can do is minimize the various defects of all real world drivers. These defects include limited frequency range, which neccessitates more than one driver, which is why crossovers exist at all, low power handling, peaks and troughs in frequency response, and so on. A well designed crossover can dramatically improve the sound of a set of drivers, but it always comes at the cost of some loss of efficiency and some effect on amplifier loading.
And of course, any crossover adds to the cost of the drivers themselves and the enclosure. Any crossover design and component costs must be recouped somewhere, and the drivers or enclosure are where those expenses can be made up. At a given price point, the more complex the crossover, the worse the drivers or enclosure will have to be. At the lower end, what might seem like a small difference in cost can be very significant (remember the rule of thumb that manufacturing costs are about a quarter, or less, of the selling price).
So it is very possible for a manufacturer for a given price to make a better sounding speaker with a minimal crossover than one with a more complex crossover.
Two other thoughts - I'd rather a manufacturer saved money by using an electrolytic capacitor than a film cap if the difference means a better driver can be used. Replacing caps is easy and cheap, whereas redesigning a speaker with the same better driver is going to cost much more.
And as a fan of Lowther and other full range speakers, I suggest listening to a good pair of speakers that use a whizzer cone before condemning speakers with no crossover (actually, no electronic crossover, since there is functionally a mechanical crossover).
