When does a subquery choose a join instead as a logical operator?

so the simplification in the algebrizer is supposed to convert some of the subqueries to inner or outer joins. for example, i tried this

DBCC TRACEON(3604)
USE ContosoRetailDW
BEGIN TRAN 
SELECT ProductKey
FROM DimProduct 
WHERE ProductKey IN (SELECT ProductKey 
                     FROM FactSales
                     WHERE SALESKEY <2) 
OPTION(RECOMPILE,QUERYTRACEON 8605)
COMMIT TRAN

the output was

-none
*** Converted Tree: ***
    LogOp_Project QCOL: [ContosoRetailDW].[dbo].[DimProduct].ProductKey

        LogOp_Select

            LogOp_Get TBL: DimProduct DimProduct TableID=117575457 TableReferenceID=0 IsRow: COL: IsBaseRow1000 

            ScaOp_SomeComp 2

                ScaOp_Identifier QCOL: [ContosoRetailDW].[dbo].[DimProduct].ProductKey

                LogOp_Project

                    LogOp_Select

                        LogOp_Get TBL: FactSales FactSales TableID=1602104748 TableReferenceID=0 IsRow: COL: IsBaseRow1002 

                        ScaOp_Comp x_cmpLt

                            ScaOp_Identifier QCOL: [ContosoRetailDW].[dbo].[FactSales].SalesKey

                            ScaOp_Const TI(int,ML=4) XVAR(int,Not Owned,Value=2)

                    AncOp_PrjList 

        AncOp_PrjList 

*******************

if I re-write it like

BEGIN TRAN;
SELECT DISTINCT dp.ProductKey
FROM DimProduct dp
JOIN FactSales fs ON dp.ProductKey = fs.ProductKey
WHERE fs.SalesKey < 2
OPTION (RECOMPILE, QUERYTRACEON 8605);
COMMIT TRAN;

I get

-none
*** Converted Tree: ***
    LogOp_GbAgg OUT(QCOL: [dp].ProductKey,) BY(QCOL: [dp].ProductKey,)

        LogOp_Project

            LogOp_Project QCOL: [dp].ProductKey

                LogOp_Select

                    **LogOp_Join**

                        LogOp_Get TBL: DimProduct(alias TBL: dp) DimProduct TableID=117575457 TableReferenceID=0 IsRow: COL: IsBaseRow1000 

                        LogOp_Get TBL: FactSales(alias TBL: fs) FactSales TableID=1602104748 TableReferenceID=0 IsRow: COL: IsBaseRow1001 

                        ScaOp_Comp x_cmpEq

                            ScaOp_Identifier QCOL: [dp].ProductKey

                            ScaOp_Identifier QCOL: [fs].ProductKey

                    ScaOp_Comp x_cmpLt

                        ScaOp_Identifier QCOL: [fs].SalesKey

                        ScaOp_Const TI(int,ML=4) XVAR(int,Not Owned,Value=2)

                AncOp_PrjList 

            AncOp_PrjList 

        AncOp_PrjList 

*******************

So, the question is: How can I get the **LogOp_Join** in the first query? I tried creating a similar table with 50 million rows still did not happen. What are the conditions that make that happen?