Join Index not getting used for left joins

Database

Join Index not getting used for left joins

I created a Join index for the below query and I am  trying to Join that query to another table. If I  use inner join then Join index is getting utilized but when I use left join then it is not getting used.

Join Index

CREATE JOIN INDEX TESBOX.JI_SECR_TBL AS

SELECT 

A.SECR_ID,

A.ASST_TY_CD , A. ASST_STYP_CD,

A.ASST_SUB_STYP_CD,

B. PROD_TY_CD,

C.PROD_TY_TX

FROM

TESTBOX.TABLEA  A

LEFT JOIN

TESTBOX.TABLEB B

ON

A.ASST_TY_CD = B.ASST_TY_CD

AND A.ASST_STYP_CD = B.ASST_STYP_CD

AND A.ASST_SUB_STYP_CD = B.ASST_SUB_STYP_CD

AND B.CUR_RCD_IN = 'Y'

LEFT JOIN

TESTBOX.TABLEC C

ON B.PROD_TY_CD = C.PROD_TY_CD

AND C.CUR_RCD_IN='Y'

WHERE A.CUR_RCD_IN='Y'

PRIMARY INDEX FINT_CSP_ID(SECR_ID)

My Query   =>

PI  for TESTBOX.FACT_TABLE is ACCT_ID , SECR_ID.

SELECT FACT.SECR_ID , FTPT.PROD_TY_TX

 FROM

TESTBOX.FACT_TABLE FACT

LEFT   JOIN

(

SELECT 

A.SECR_ID,

A.ASST_TY_CD , A. ASST_STYP_CD,

A.ASST_SUB_STYP_CD,

B. PROD_TY_CD,

C.PROD_TY_TX

FROM

TESTBOX.TABLEA  A

LEFT JOIN

TESTBOX.TABLEB B

ON

A.ASST_TY_CD = B.ASST_TY_CD

AND A.ASST_STYP_CD = B.ASST_STYP_CD

AND A.ASST_SUB_STYP_CD = B.ASST_SUB_STYP_CD

AND B.CUR_RCD_IN = 'Y'

LEFT JOIN

TESTBOX.TABLEC C

ON B.PROD_TY_CD = C.PROD_TY_CD

AND C.CUR_RCD_IN='Y'

WHERE A.CUR_RCD_IN='Y'
)FTPT

ON FACT.SECR_ID = FTPT.SECR_ID

WHERE

FACT.EDW_CUR_RCD_IN='Y'

AND CLIENT_ID='C01'

Any suggestions pls .