Why are there no wheel studs? Why instead, do I thread a lug bolt into a hub?

I do not understand the thought process behind it.

Pics, in case I'm crazy...

 

All 12A cars were made that way. In fact, I believe all mazda cars were that way until the mid 80's. Many cars have used that type of setup, including BMW, VW/Audi/Porsche, and many older US models.
You can get screw in studs, if you really want to do away with the bolts.

 

just curious as to why. I like it, personally.

 

I spose it was cheaper. 1 bolt prolly costs less than a stud/nut combo.

 

I suppose.

I am guessing the downfall happens when you break one? Because you can't just take a sledge hammer and pop it out.

 

Dunno. My car came with custom wheels, that also included special bolts that are 1 piece. They also caused me to buy another lugwrench, as they only have a 17mm hex.
I've heard horror stories about the factory lugbolts popping the end off, though..........

 

You never want to go though that.

 

The way the brake system is built the holes are integral to the front rotors. If they used studs with the hub/rotor design then we would have had to replace the studs with each brake rotor. Not that there are not design solutions to that problem, but it all comes together in a way that makes it easier for the manufacturer to use a bolt.

The darn heads come off the bolts fairly frequently. The trick is to take one bolt/head apart and save the head. Then you can just pop the head on if a head falls off the wheel, and easily take the bolt out and discard it. Or, pound it on with red lock-tite added between the head and the bolt and use 'em for another 100 K.