I have a theory, zero evidence but it’s sort of backed by what’s written in the DM article :
‘Quite how seriously the Duchess of Sussex took the 2019 letter from Ms Loveless is, at this stage, unclear. In February 2019, shortly after it arrived, Meghan authorised five friends to brief her favourite outlet, People magazine, about her estrangement from Thomas Sr. The resulting article suggested the Duchess wished to repair the relationship.
Later, in a 2022 Netflix documentary, Meghan declared that she had been 'a daddy's girl my whole life'. She only appears to have categorically cut him off in late 2025, when Thomas Sr was gravely ill in hospital in the Philippines.’
I think that when presented with this letter, asked about the possible veracity by the Met, Meg may have suggested that because this is the ex wive who is a drug user etc, that its just malicious ramblings.
Which the Met has then decided, there’s little credibility and therefore didn’t meet the standards to refer to Interpol.
This could be why Meg continues her alternative narrative about why she cut her dad out for up to 4 years after she seen this letter. The People article where she remains open to the idea of reconciliation, NF docu where Harry says it’s his fault, the Oprah interview where she states she lost her father because of the media circus.
If she cuts him off clearly in 2025, then something else could have happened between the years of 2022 and 2025 to make her believe that what was said in the letter is true and to stop with the alternative story she had been banding about.