The SUV category contains two fundamentally different structures. One derives from car engineering and the other from truck engineering, and almost every characteristic follows from that.
Body on frame separates structure from body
A ladder frame carries the suspension, drivetrain and towing loads, and the body is bolted to it through rubber mounts.
Because the frame handles structural duty, the body can be simple, and the same frame can support several body styles including pickups and cab chassis variants.
The rubber mounts isolate the body from frame flex, which is useful over rough ground but permits movement that a rigid structure would not allow.
Unibody makes the body the structure
A unitary body integrates structure and skin, with loads carried by the shell itself and suspension attached directly to reinforced points within it.
This is stiffer for a given weight, which improves handling precision, ride refinement and noise, and it allows a lower floor and better interior packaging.
Crash structures can also be engineered more precisely, since the load paths are designed as part of the shell rather than shared with a separate frame.
The difference shows up in towing and durability
A ladder frame handles concentrated loads at a towbar well, because the load feeds directly into a beam designed to carry it.
Frames are also easier to repair after deformation and tolerate sustained heavy work, which is why commercial and remote-area use still favours them.
Unibody vehicles tow competently at moderate weights, but their capacity is generally lower and the structure is less tolerant of repeated overload.
Off-road behaviour differs in character
Frame vehicles typically use a live rear axle and long-travel suspension, keeping wheels on the ground over uneven terrain and offering simple, robust geometry.
Unibody vehicles usually use independent suspension, which gives better on-road control and less articulation, though electronic traction systems compensate substantially.
Ground clearance and underbody protection are more a function of design intent than of construction, and both types exist in capable and unsuitable forms.
Repair economics differ as well. A deformed frame can often be measured and replaced as a component, while a damaged unitary shell requires sectioning at manufacturer-specified points, which is more precise work and more likely to end with the vehicle being written off.
The market has moved decisively toward unibody
Most vehicles sold as SUVs are now unibody, because most buyers use them as tall cars and value ride, refinement and efficiency.
Efficiency regulations reinforced this, since a lighter, stiffer, lower structure is easier to make aerodynamic and economical.
Body on frame persists where the capability genuinely matters, and the two now serve visibly different purposes despite carrying the same category name.