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Academia has always forced grad students to attempt innovative research. The core requirement of a PhD dissertation is "novel findings"—e.g., something completely new.

Apprentices work on papers and research for their professors. No one is incentivized to do replication work: either you replicate it successfully (great) or you find flaws. In the latter case, you'll probably be a nit-picker anyway—also not really additive. On the off-chance that you refute a high-profile study (e.g., some of the outright instances of fraud), you might get some recognition, but now your name is associated with something negative (e.g., fraud: "X is not true") vs. positive ("X is true").

Finally, this is some of the role of review panels in journals: too pass the burden of proof.