Scouting implements are expensive and fragile. When push comes to shove the robot can defend itself, but it's risky and looks pretty bad on cost-benefit analysis to use the scout robots as fighting robots.
Not every situation can or should be solved by killing all opponents. Maybe they have hostages or fragile cargo, maybe they can be negotiated with, maybe there's some intel that can- or has to be recovered. Scout robot frame cannot handle the power draw for an AI capable of making these decisions, but humans are perfectly capable.
