Water resistance does not mean what people think. ISO 22810 says that a 3 bar (30m) water resistant is “Not suitable for showering, bathing, swimming, snorkeling, water related work, fishing, and diving.”
30m. Not. Suitable. for. showering.
Also, most really waterproof watches, 100m+, have small circular metal cases with metal backs that are screwed shut against a gasket. Some, like G-Shocks, have a proportionally thick stainless steel backplate screwed down, but the plate is what? 3 cm. Diagonal?
Doing so on a thin rectangular device with a reasonable cost is near impossible, too much flex.