Plastics are nonpolar and water is polar. Like dissolves like. Therefore plastics dissolve in nonpolar liquids, like toluene. Plastics are usually made of only carbon and hydrogen bonds, which normally give rise to nonpolar compounds.
By dissolving the alkali in the glass composition, a porous surface is left that consists of the silica network with holes where the alkali has been removed by the acid. Corrosion by water is similar to acid corrosion in that alkali is removed from the glass surface. Water corrosion acts at a much slower rate.