Scalextric at least came with everything you needed to play with them (except a power controller).
Train sets on the other hand contained hardly anything in the box and the Dublo range was a particularly poor example of this and still is. The locomotives themselves were superb and still are but the cardboard box they come in probably has more play value than the train sets themselves.

Modern trains sets are a little better in that respect but the basic idea is still to get you to spend hundreds of pounds more before you achieve anything like a usable layout.