Because with `r0` you're liable to just parallel evaluate to the thunk containing the computation you're trying to parallelize, and the actual computation then takes place later *outside* the parallel section?  (That is, what comes out of parList is a list of the thunks passed to `r0`, otherwise unevaluated.  You wrapped them in an `id` and then parallel evaluated the `id` away, real useful that. :)  You need to go at least to WHNF, then it comes down to the strictness specified in what's passed to `rseq`.

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