Why the very first module implemented in many ERP systems is Financials module?

Financial module impacts all others modules. It also provides the basic pulse of an organization. Other modules cannot be implemented without the financial module in place. Successful implementations of financials show up immediately reinforcing the faith of an organization in ERP. All these factors explain the fact that financial modules are taken up first.

ok, erp systems are built to keep records and generate reports for every tiny transaction took place in the organisations , financial modula has the backbone for all other modules this is COA the chart of account which is connected to Goods \\ inventory - payroll for example which should account the transaction into financial records

in other meaning everything is money !

Another reason I would add taht almost all other modules records tranactions having a financial impact and without a financial module implemented at first palce, a combined financial picture of the whole business can not be drawn.

Because Financial module setup is more connected with the Multi Org and sets the back bone for the business processes in terms of Ledger- Legal Establishment-Operating Units etc. Also, the Oracle Ebiz configuration model , licencing etc also demands FIN to be first and atleast lean.

Because it was the first set of business processes to be automated and it is the functions that is avialable in all types of businesses.