How come some component float variables can only be set in Construction Script (and Not Event Graph)

It seems that some float variables from some components can only be set in the construction script. Is this true or am I missing something? I attached a quick example of the initial speed variable in a ProjectileMovement component. In construction script it updates the speed correctly, in event graph it does not do anything.

Even if I create another float variable and use that to set the initial speed variable, it works as long as it is in construction script but editing that variable in event graph does nothing.

I am confused because there is numerous other places in my projects where I have set the float variables on components in event graph with no problem. Any insight into this is appreciated.