The younger clusters do not. Apparently, main sequence stars become red giants when they run out fuel. This conclusion can be supported by other more detailed arguments also, of course. The most important of these is known as 'computer modelling' of stars. Let the laws of physics take over.
Gravity makes the atoms attract each other into a smaller and smaller space.
At that point the cloud of atoms has become a star. This scenario is modelled with computer arithmetic-hence the name. The arithmetic shows that the number of atoms in the original bunch determines the temperature at birth. The more there are, the hotter the star. That, of course, is exactly what is observed for main sequence stars as the mass-luminosity relation.