What's the height differential between the garden surface and the garage floor? Acco drains will intercept surface water, but not groundwater. If you removed the drains, the soil underneath is still wet. The weight of this wet soil creates hydrostatic pressure which squeezes the water into nearby structures. Any crack is an easy path for water ingress, but concrete itself is porous so a couple of feet of wet soil will create enough pressure to cause penetration.

Did you install sill plate gasket under the framing's bottom plate?