Everything is disposable, including people. When we no longer have use for things we get rid if them. The same can be said about people in our lives, even family members.
It doesn't take much to get booted these days. There's no such thing as a friendly disagreement anymore when opinions differ, especially about politics.. Grandpa voices his opinion and son-in-law voices his, and before long it explodes. Reconciliation is off the table and now grandpa and grandma are alienated from future family visits.
The parents get rid of the person instead of the problem.