Yes, they can break. They can become a source of leaks and body rot. They add to the weight of the camper. Campers are already poorly insulated. Slides add to the surface area and heating/cooling issue. Slides often made it difficult or impossible to use the camper without extending the slides. Slides cannot be used in parking areas, on the street or in small camp sites.
One of the biggest issues is the truck needed to carry all that weight. As the weight grows the cost of the truck needed also jumps. With the weight the minimum truck is a 1 ton usually a dually and with anything but flatland use, you will need a diesel. A suitable new truck will cost around $70,000. Bigger truck campers with multiple slides can easily mean a truck beyond the 1 ton rating and another jump in cost. All that weight also limits the user to paved or well maintained gravel/dirt roads.