Sheaths are often lighter and less bulky then scabbards of the same length and width. As well as easier to construct, maintain, and repair than scabbards are. However the added weight, complexity, and bulk of a scabbard comes with a greater level of long term protection for the implement. This tends to make sheaths better for tool application. Wherein a craftsman/laborer might be frequently maintaining the implement anyway as part of it's regular use. And can often have full control over the environmental conditions the whole will be exposed to. Therefore the sheath only needs to offer interim protection between maintenance and use.
However scabbards are typically better for weapon application. Wherein a soldier/warrior might need to transport the implement over long distances. With the whole's environmental treatment largely outside of their control or unpredictable. And where most of the time the implement will not be in use. More long term storage and less time for maintenance with only occasional usage, necessitates a higher preservation of initial condition of the implement. Given the nature of modern warfare and the greatly reduced likely hood that the common man is going to be involved in civil combat with a bladed and edged weapon.
Scabbards for practical purposes have largely fallen wayside. And are mostly seen when newly produced as part of reproduction or novel weapon offerings. Whereas sheaths have maintained their popular use. Not only through the constant and non-declining need to protect tools. But through lower manufacturing costs.
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