Why do train tracks have sleepers and ballast beds, while high-speed rail tracks only have ballast beds without sleepers?

in short, these are two types of technologies.

High-speed rail generally adopts monolithic ballast bed, which is equivalent to combining ballast bed and sleeper.

it seems that you have no sleeper, but in fact the effect is the same.

Because before ordinary railways generally used gravel track beds, it was troublesome to lay them, and it was easy to be washed away in case of floods or something. The advantage is good elasticity, but because it is gravel, sleepers must be added to pave the track, otherwise the power of the train cannot be dispersed to the track bed. The disadvantage is that the deformation is relatively large.

High-speed rail directly turns the gravel into a large piece of concrete. Of course, the track can be paved directly, because there is no need for a separate sleeper to disperse power, and this large piece of concrete can directly bear the weight of the train.

In fact, the types of ballast beds are applied flexibly according to the situation. Integral track beds are also used on ordinary railways. Although most of the high-speed rails are monolithic ballast beds, some of them also use gravel ballast beds.