Thumpalumpacus
Major
Putting more engines on a dive-bomber increases the practical weight of the aircraft as it pulls out of the dive. A 2-G pullout doubles the weight the airframes thinks it is, and you have to structure for that.
Now put those engines out on the wings -- which is more weight in and of itself -- and then add in the extra weight for the load-bearing members to keep the wings from flying off due to the extra leverage the weight location adds, and you end up with something that might drop a good load, but cannot go too steep, and has its level-flight performance impaired dragging around all that reinforcement. Of course, if the dive is accurate enough it can still perhaps crash into the target.
It's about trade-offs. It's why you didn't see too many twin-engined dive-bombers.