亻 is the left-side form of 人 (person). Here it points to a body - 僵 originally described a corpse stiff with rigor mortis, the literal frozen-person sense that broadened to any rigid, deadlocked situation.
畺 supplies the sound jiāng directly - two fields stacked between three boundary lines. Same phonetic in 疆 (jiāng, frontier) and 缰 (jiāng, rein). The fixed-boundary imagery also reinforces the rigid, immovable feeling of 僵.
