If 4 drops is a low bound, couldn't they have aimed for say 10? Can't you draw 10 drops of blood relatively easily from the finger? I feel like I've had that done before when donating blood. It'd still be a much less annoying process than vials after vials like it seems like most blood testing is.
It's hard for me to imagine they wouldn't have said "well, one drop didn't work but we could decently with four but we won't do that."
It is really hard to get more than a single drop out of fingerprick. The reason why is the capillaries close up very quickly - if you are really lucky you can get 2 drops out, but anything more is a struggle.
The second problem with fingerprick blood is you pick up quite a bit of skin tissue in the process, but the amount collected is quite variable. What you end up measuring is blood + some unknown percentage of skin tissue derived material. None of these things are good for reproducibility.
It's hard for me to imagine they wouldn't have said "well, one drop didn't work but we could decently with four but we won't do that."
I haven't followed tremendously the story though.