Do you imagine that Apple has finite engineering resources? The last I heard was it is the richest company on earth. They’re just satisfied with the status quo in which Google does all of their security work and nobody cares because of decades-old misperceptions about Mac vs Windows malware safety.
Money alone doesn't create more qualified engineering applicants. They may be able to use money to poach those resources but the candidate pool for this sort of work is extremely finite.
