I think the difference is that in an intact family situation.. what is left to the spouse (or what's left).. would most likely be left to the kids. ... but when it's a "2nd" wife situation, especially one where she has her own kids.. it's very possible for her to exclude her husband's children from any inheritance.. and point it towards her own preferred Heirs instead.

Honestly, it happened to my father.  He was one of 4 brothers by his father's first wife.  She died when they were fairly young and my grandfather remarried and had another child with a woman who already had one child from a prior relationship.  When my grandfather passed.. his wife basically got "everything".. (even tried to get the boys to pay her for their private school tuitions and changed the locks while they were at the funeral!).  She died in the past 5 years and everything she had was left to HER two boys.. nothing to my father or the families of any of the other three brothers.  My grandfather was pretty well off she inherited a condo in the same building where Oprah had a place.. it was not an insignificant amount of money.  but.. the brothers were pretty  much left out in the cold.

And.. even with that.. my father actually did maintain a good relationship with her and his half brother.. and I don't think he ever resented it.  but I'm not so sure I would be as unbothered by it if I was in my father's shoes... because while I get that no one is OWED money from their family.. it's generally many families' goals to build wealth to pass down to future generations.. and steplife moves some of that to other people.

Even on here.. we see people who want to see how they can ensure their bios benefit but not stepkids.. or want their spouse to have use if they need it but have their own kid inherit their share.

So.. in this way.. I can understand the concern a skid might have to see thier stepparent get something that they know will likely never make it down to them.