Files to look at:
By default, the HTML form collects information from all hidden inputs and posts it to the Controller. DataGrid is not an editor and doesn't have a hidden input. As a result, model values assigned to the grid's DataSource option are not passed to the server out of the box.
You can manually create hidden inputs for each row at runtime, place them onto the form and specify their name attribute as demonstrated in the "Model Binding in ASP.NET Core -> Binding to Collections" help topic before it is submitted.