Get all implementations types of a generic interface

I'm trying to get all the implementations of IEntityModelBuilder with the following code, but instead it returns an empty collection.

public class EntityFrameworkDbContext : DbContext
{
    //constructor(s) and entities DbSets...

    private static IEnumerable<IEntityModelBuilder<IEntity>> _entitymodelBuilders;
    internal static IEnumerable<IEntityModelBuilder<IEntity>> EntityModelBuilders
    {
        get
        {
            if (_entitymodelBuilders == null)
            {
                var type = typeof(IEntityModelBuilder<IEntity>);

                _entitymodelBuilders = Assembly.GetAssembly(type).GetTypes()
                    .Where(t => type.IsAssignableFrom(t) && t.IsClass)
                    .Select(t => (IEntityModelBuilder<IEntity>)Activator.CreateInstance(t, new object[0]));
            }

            return _entitymodelBuilders;
        }
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        foreach (var builder in EntityModelBuilders)
            builder.Build(modelBuilder);

        base.OnModelCreating(modelBuilder);
    }
}

internal interface IEntityModelBuilder<TEntity> where TEntity : IEntity
{
    void Build(DbModelBuilder modelBuilder);
    int BuildOrder { get; }
}

//sample implementation
internal class UserModelBuilder : IEntityModelBuilder<User>
{
    public int BuildOrder
    {
        get
        {
            return 0;
        }
    }

    public void Build(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<User>()
            .ToTable("users")
            .HasKey(e => e.Id);

        modelBuilder.Entity<User>()
            .Property(e => e.Id)
            .HasColumnName("id");

        modelBuilder.Entity<User>()
            .Property(e => e.Email)
            .HasColumnName("email");

        //and so on...
    }
}

If I change the type with

var type = typeof(IEntityModelBuilder<User>);

the types fetching code runs fine and returns the expected UserModelBuilder. How can I do this with generics?