They are built differently that's all. The insulating pins are put on the section of rail that normally is "dead". The wheels complete the circuit by forming a connection to the "dead rail". this connection leads to the turnout coil. The turnouts switch coils other end, connects to the center rail.
Early 0-27 turnouts used a small slice in the outer rail. It was soon changed to the inside rails eliminating the slice seen on the early ones.(warning large trains and long cars cannot all run on 0-27. In a curve, the overhang hits the linear motor housing on the turnout.
(some other people/forums only use the correct term, turnout. Ask me how I know
)
O gauge is taller, and was made from heavier, thicker, metal (new?)
If you mix them plan to smooth the height transitions. Use adaptor pins unless you're willing to "tin knock" them into the correct shape.
My Marx bottom out on some Lionel 0-27 turnouts. On a plain loop they are fine. Marx and Lionel have bigger incompatibility issues in turnouts, drivers gear hit, and flange bumping.
