Presumption of Invalid Gift
A testamentary gift to the person who drafted the instrument, is in a fiduciary relationship with the decedent, a care custodian of the decedent, or related to someone falling into one of these categories unless the person receiving the gift is a relative of the decedent is presumed to be procured through fraud or undue influence, and is therefore invalid unless the presumption is rebutted (Probate Code section 21380).
The reason this rule exists is because undue influence is insidious. It is almost always done behind closed doors and very difficult to prove. Therefore, when someone has such a position of authority over someone, like a care custodian, it is incredibly likely that individually can manipulate the decedent to do whatever they want them to do. The legislature acknowledging that decided to get rid of the old rule that required someone challenging the validity of the gift to show that the disqualified person took an affirmative step in procuring the instrument before the presumption kicked in.
Because this led to the California Supreme Court decision requiring a showing of active procurement, not just the suggestion of ideas (which can be more than enough for someone in such a position of power).
That is what the legislature was reacting to when they created the new rules regarding a disqualified person.
To analyze the new rule itself, you have to know who is disqualified. The first two categories are self-explanatory; however, the third category actually has a specific definition that is counter intuitive to the lay definition of a care custodian.
Generally, a person that cares for an individual is only disqualified if they get paid to do so and the person they are caring for is 65 years old or older and has mental deficiencies that makes them susceptible to undue influence or cannot properly provide for their own personal needs (Probate Code sections 21362 and 21366).
Once someone is deemed to be disqualified from receiving gift, they then must prove through clear and convincing evidence that the gift they received was not due to fraud or undue influence. This is an extremely difficult burden because it forces the individual to prove a negative.
To help show the tremendous challenge this faces, try this thought exercise: Prove to me you have never stolen something in your life. How would you do it? Would you go through your criminal record to show that you have no conviction of stealing? That would only prove that you were never caught. While not as onerous as the hypothetical I presented, the only way you could likely succeed in proving that the gift was not obtained through fraud or undue influence is if the decedent discussed their testamentary instrument repeatedly to multiple people and there was almost always someone in the room with the disqualified person when the disqualified person was with them. Otherwise, there is no way to corroborate what the disqualified person says and therefore they would likely fall short of clear and convincing evidence.