GRollins is right, about the cost issues. The budget end of the market is extrmely competitive, and the more 'audiophile' brands will often sacrifce some margin to get you in, hoping to make it back when you upgrade later.
BUT, how do they sound? If they are good sounding (wrt pricepoint), and they only have simple crossovers, that tells me the designer did a good job optimising all the parameters. I have yet to find in audio that making something more complex, beyond what's neccesary, makes it sound better.
For example most 6" mid-basses will start to break up somewhere above 2.5kHz at moderate levels, with metal cones being the worst usually. If you don't want to hear all that rubbish, you have to either(a) use higher order, more complex x-over (b) tweeter that will work at lower frequencies (c) better mid-bass with simple x-over. Drive units only work in a limited frequency range, and the drive unit's deigner must make lots of decisions and compromise the performance in some areas even in very high cost / high performance drivers. My mid/high Pro drivers cost $US1500 ea, and I only use one cap to cross them over. That's all they need.
Then of course, there are Lowther, Fostex, Goodmans, Diatone, Eminence etc drivers that need no crossover at all.