Yeah. Wouldn't be surprised if some of the internal argument goes: Why pay Sainz €20M when Perez brings that money through sponsorship. They might've even budgeted the new wind tunnel based on expected income from Perez's sponsors, not having to take it from all Red Bull Gmbh.
And then they figure..
Perez performs 3 out of 5 times.
Sainz performs 4 out of 5 times.
I'm sure there are a lot of angles being reviewed many of which aren't absolute on-track performance based. Too bad for us fans who want something different.