Tracer BBs show exactly where you are and you can't just shoot 10 in a row. Using them actually makes the game harder to play.
Another reason is the demand. They are too expensive compared to quality bbs plus you need tracer unit.
for indoor play, I prefer to run .20 or .25 for reasons of speed but the lowest tracer bb i have seen is 0.25
AW Hi-Capa 5.1 X 2
EMG DD MK18 Cerakote
VFC M4 MK18
TM MP5 First gen
TM MP5A5 with swordfish 2004