Q1: 

Why does cash flow limit to select bank or cash journals only?

Answer 1:

Bank and cash reflect money comes in or out. Only at this timing, the cash flow statement will reflect the transaction

Q2: 

Why does accounts such as expense show on the cash flow statement bank or cash journal? Expense account doesn’t exist in any bank or cash journal? 

Answer 2:

Cash flow statement shows the counter part account (counter part of cash/ bank/ outstanding receipt/ payment, but exclude AR/ AP). See next page example.

Create a bill $100 (Expense vs AP) 5/23/2022. No transaction on CFS. Register payment 6/25/2022 $100. Transaction reflected on CFS. (Not AP, not outstanding payment but expense account (account tags: Operating activities .