They fund founders with the immutable qualities which correlate with success. These include
1. FAANG or Ivy/Stanford/Harvard pedigree
2. Ex-founder with a good exit
3. Physically attractive/charismatic, a good salesman
4. Extremely high intelligence, ability, track record of aptitude
These qualities are more important than the idea of the company, which they expect to pivot or evolve over time. What doesn't change over time is the founders' relative advantage over their peers in these aspects, so it makes sense to prioritize them in selection