Glass Mapper loads collections only for interfaces

Using Sitecore 10.2 and Glass Mapper 5.8.180

After upgrade from Sitecore 8.2 and switching to above mentioned version of Glass Mapper our code stopped loading collection references. I am aware that in Glass Mapper now the lazy loading is turned on by default and I want to keep this setting.

Problem is with follows:

Having

[SitecoreType(TemplateId = "{...}", AutoMap = true)]
public interface IStatementContainer
{
    IEnumerable<Statement> Statements { get; set; }
}

public class StatementContainer : IStatementContainer
{
    public virtual IEnumerable<Statement> Statements { get; set; }
}

The following code

_mvcContext.SitecoreService.GetItem<StatementContainer>(datasource)

does not work properly. The Statements are empty.

For following code

_mvcContext.SitecoreService.GetItem<IStatementContainer>(datasource)

the Statements are being loaded properly.

Could you explain me the difference in behavior?

Our legacy code contains a lot of usages of concrete types rather than interfaces, changing all of them would be difficult.