*My 'uncle'. I use the term loosely.
My paternal Aunt and he were my godparents, been in my life every step. Christmases, birthdays etc. Aunt called me most weeks, doted on my children etc. Aunt sadly developed cancer and died aged 57. Uncle ghosted us then eventually cut the whole family off and never contacted us again. My children, who loved him to bits, were devastated and couldn't understand why.*
I realised at that point that my 30 year relationship with him was just a facade to placate my lovely Aunt.
Obviously, I'm a stranger and don't know the dynamics, but I agree with PP that his behaviour might well not be deliberately unkind.
He might have always seen his role in the family as having arisen because he was married to the blood-member of the family, and now that she has gone, he may even feel like he doesn't have the right to be part of the family any more - like he was an outsider, allowed in by association, and now an outsider again.
Maybe he's utterly devastated and the thought of contact with 'her' family pushes him right over the edge. He might even deliberately be trying to forget her too - possibly hating himself for doing so - if the pain of remembering her is just too raw.
He might have found love again with somebody else and think you will consider him a traitor to your Aunt's memory and thus disown him in disgrace anyway.
More mundanely, it might not be any kind of active desire to 'ghost' you, but a lot of men depend on their wives to manage their whole social calendar, make contact and keep the relationships going. They're very glad to come along and do love spending time with everybody, but they're just utterly hopeless at doing anything off their own bat.
I myself have an Uncle like this - he's a nice man and we spent a lot of fun time together when we and our cousins were young, but since my Aunt (the blood relation) died, we just don't really seem to have any link, so the channels of communication have just ended up closing organically. I don't have any real contact with my cousins now either; if I see them on the very odd occasion at a funeral, we get on well, but they have their lives, I have mine and they just don't really correspond any more, now that the links - their Mum/my Aunt and my Mum/their Aunt are no longer with us.