Are you referring to shibuta? It has Rava’s Certification not the OU’s
“Just because Your Bubbie and Zayde didnt eat something is no reason to Assur it. ”
Nobody (as far as Im aware) says it s actually assur (if properly checked etc). But it shouldnt be that shocking that people who maintain their parents dress also avoid any “new” foods. why is avoiding suchi any stranger than wearing a fur hat in July, or for that matter a fedora.
Dont try to ask these using logic. IT isnt a logical decision per se. But it helps some maintain a connection to the past. It is a hergesh and not one based on historical factors
Plus it is an easy way to be frummer than other people. so win win.
If you enjoy sushi nobody is stopping you (yet)