But you can't fuel up the solids on the pad. You must cast the propellant into the casings at the factory, potentially on the other side of the globe if that's where you have the nearest capable industry.
This means you need fire safety everywhere, and heavy ground equipment too for lifting and attaching and assembling the solid rockets.
Meanwhile, you can fuel a liquid rocket at the pad, meaning it's empty and light and can not explode or burn during transport and handling.
So solids cause heavier rocket ground infrastructure and more danger.
Of course, with liquids you need the fueling infrastructure on the pad. It probably comes to a question, not only of scale, but also of launch rate.
In theory you could have mobile trucks fueling missiles here and there. That's how you do it at ship ports where you don't want to invest in ground infrastructure.
This means you need fire safety everywhere, and heavy ground equipment too for lifting and attaching and assembling the solid rockets.
Meanwhile, you can fuel a liquid rocket at the pad, meaning it's empty and light and can not explode or burn during transport and handling.
So solids cause heavier rocket ground infrastructure and more danger.
Of course, with liquids you need the fueling infrastructure on the pad. It probably comes to a question, not only of scale, but also of launch rate.
In theory you could have mobile trucks fueling missiles here and there. That's how you do it at ship ports where you don't want to invest in ground infrastructure.