Originally, slides were called "tip outs". That's because that's exactly what they did. They laid flat on the trailer floor and were hinged at the floor edge. To deploy you actually "tipped" them out into their functional position. Supports were sometimes necessary on these as the RV walls were not built to support the weight of the "tip out" and the occupants.
There may be some units still out there with tip outs but a modern engineered "slide out" does not need any support other than that provided by the engineers and manufacturers in their design and build.
Just like there is no need to use "RV" toilet paper folks still make it and other folks still insist it is necessary.
