Since WAT -> WASM is already easy to do, compiling <otherlanguage> to WAT makes it really easy for people to create their own abstractions for writing WebAssembly in nearly _any_ other programming language, not just those that can compile directly to the binary format.
It's also just as easy to get WASM from WAT as it is WAT from WASM. I don't know of any languages that compile to WAT and then compile to WASM; as far as I know 100% of languages compile directly to WASM.
The translation between WAT and the binary format is lossless, so there's no advantage of producing WAT as an intermediate step.