When the 2019 letter alleged to be from the 'x wife' was received Meghan was pregnant.
Any fool would have foreseen that the issue of Meghan's estranged dad would be a focus after the birth as people would be questioning how she could be so cruel in not reconciling with the dad she'd praised so much so he could meet his grandchild.
That letter at that time was insurance for when she was 'forced' to speak out about why she never reconciled with him.
I don't think they expected him to last so long after the TWO heart attacks he had in 2018 and imagined this would come out after his death because maybe doing it while he was alive was a step too far even for Meghan.
Time creates distance though, emotions dim, and when you're too skint to pay the billionaire lifestyle bills, needs must.
At the time that letter was paid for sent, HAM couldn't have foreseen that they wouldn't get their way of not having to open factories in Dagenham and only dipping in to do the glamourous bits. They were arrogant enough they assumed they would be able to do what they wanted. They assumed they'd be based in the UK and the pressure to give a feasible story about ostracising her Dad to invoke pity would be much greater here as she was much more visible (as she wanted to be) than she was in the US.
I think Meghan had absolutely no intention of her father being a part of her life after marrying into the RF. Whether that be because of embarrassment of his 'hillbilly' style or that he knew stuff from her past she didn't want getting out.