The article sorta hints at it, and my half-ass guess is that it was more practical to dig the Canal to a certain depth and pump more water in to make it ‘deeper’, than dig to depths adequate for huge ships they perhaps wouldn’t have envisioned in 1904.

Assuming each lock is effectively watertight, that’s fairly clever engineering, but it assumes a perpetual supply of water.

Disclaimer: I’m a high school dropout, so wutdefuquedoIknow?