This has been happening for years now. Random feet, still wearing a sneaker, wash up on a Canadian beach.
This has been explained, at least to an extent....
Say a person is fishing, boating, hiking, whatever.... and falls in the water and drowns....
The body floats, then sinks, then generally bloats, refloats, then sinks again.
Slowly it begins to decompose, and when it has sufficiently disintegrated, any buoyant accessories
(like, say, athletic shoes or sandals with foam-nased soles) float away, and they're carried (foot and
all) by the ocean current until they wash up somewhere.