It is partly an issue of availability, if you are looking for a small car that is RWD you pretty much have two choices, and unless you are building a purpose built car where you can get away with using a gutted shell, neither are particularly cheap.
There are tons of small FWD cars available for next to nothing. The concept is the same, add power and torque to a vehicle to make it faster, and whether you like FWD or not there are some wickedly fast FWD cars out there.
Of course in the vein of your question, why would somebody bother with drag racing anyway? it is kind of boring, you go in a straight line for a quarter of a mile (or less). When you are dealing with something that is more of a hobby with mega corporate support, it all comes down to personal preferences and whims. I would imagine that there are plenty of guys who go the FWD route just because they want to see just how fast thier econobox can go. Decades ago most people were wondering why would anybody bother to put modern V8 into an old T or A coupe, when there were so much more powerful and fast cars available. Why did the rodders in the sixties build T Buckets when they could have went down to the dealership and bought a new GTO or Mustang for about the same money?