In your opinion, are they a whale because they make a great product... or just have a great marketing/PR/sales team? I am guessing "great product" because I cannot believe that Google cannot just rebuild it themselves (if not a great product).
To answer your question. Google doesn't acquire Wis because Google can’t build a comparable product themselves. The real driver is that Wiz has already achieved market penetration and trust. Replicating that from scratch would be a massive undertaking, requiring not just a sophisticated product but also the brand credibility, customer relationships, and reputation for reliability. establishing that level of traction and trust is difficult, time-consuming, and expensive. I highly doubt Google would try to build a direct competitor from the ground up when acquiring Wiz allows them to leverage its existing success right away.
Regarding your google comment: Google builds Google products that can also be used by other people. I am pretty confident they cannot build something like Wiz. And not because they don’t have researchers and developers.