Exadata is older than the Sun Aquisition
The original Exadata was a join venture with HP, but Oracle switched to Sun SPARC to internalize all of the revenue.
While the split of Query and Store engines is similar to MPP, Exadata sold well because it was simpler and cheaper to deploy than an equivalent Oracle RAC cluster. cheaper because you didn't need a full license for store nodes, simpler because it had its own infiniband fabric within the rack.
The cold hard truth is that servers with 100s of cores, Tb of RAM, Eb of SSD are commodities; whatever RDBMS you run on it