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For me personally this is the selling point, as I can fund their (open source) work rather than sending money to some company that does not contribute to open source. And since everything they offer is based on FOSS, migrating to another provider is easier than for closed source competition.
That said, I get your point. It is a corporation, and it is putting several eggs on one basket.
Internet Archive Scholar is somewhat different, perhaps more archival and less up to date on the latest research, but it’s pretty neat.
That said, Google Scholar is the only Google search I still default to. Haven’t found a good alternative yet.