Why is there no set with much RC Straight tracks?
According to Brickset there are 8-8 straight track pieces in both of these sets:


7896
7499


This seems to be the maximum amount, even the large complete train sets do not contain more than 8 straight tracks.

You might have more luck purchasing them piece by piece from other AFOLs, or see if there is a Pick-a-brick shop in your area.