This joint carries the burden of the whole body.
The ankle joint comprises of two layers of bones, to create a multi-directional joint that can balance the body and keep it level and stable, but this requires decent strength from the body above to hold it in alignment. If the ankle joint is strained it will become unstable which will put extra load on the foot structure as well as the shins, knee, hips and back.
If balance up the body is not good due to core strength being weak then this will also put the load down the chain on the ankle and cause the arch of the foot to collapse which can lead to bunions and all sorts of bad things.
The ankle is however supported from above, but effectiveness does depend on a good foot structure, hence the importance of a proper Assessment to establish where the instability is coming from.
Below you can see left ankle weakness due to an injury/ break: