Legal records were created for those living at the time. Not as a genealogical record for the future.
Be careful reading too much into children who are “left out” of a will and testament. The reasons may not stem around family drama, hard feelings, or ill-will. It could be that the child had simply received an inheritance earlier in their life. That child may be given a token amount in the will (such as a dollar or a few shillings) not as a slight, but rather to indicate they had not been forgotten. Sometimes a will may specifically state that the parent had already given the child money.
Of course, children are left out of wills due to “family drama.” Sometimes there is evidence of that drama in petitions to deny the will, court battles over the estate, etc. In some cases there may be mention of the family drama in the newspaper when the case was being heard in the local court.
But don’t assume there has been a falling out because your ancestor left a child out of his or her will. That may not have been the case.
It’s worth remembering that a will was an instrument for estate planning, not for leaving a complete genealogical record.