If ELAC 1 is under MEL why is it a NO GO item when carrying out EDTO on the A320?
Basically, operating ETOPS/EDTO takes into consideration worst-case scenario situations (EMER ELEC CONFIG) where you will only have ELAC1 working.
In addition, its mentioned that ELAC2 in MEL is a NO-GO item due to the logic behind the system operation where it will allow ELAC2 to work first always, and in case ELAC2 fails ELAC1 will take over.
According to :

A320 FCOM ATA (27-10-20) Architecture (Pitch control). In normal operations, ELAC2 controls the elevator and the horizontal stabilizer, if a failure occurs in ELAC2 the system shifts pitch control to ELAC1.
A320 QRH ABN-18 ELEC (ELEC EMER CONFIG SYS REMAINING), In the emergency electric configuration the ELAC2 wouldn't be available when the emergency generator is running and ELAC1 will be the only available.
A320 FCOM ABN PRO (ELEC EMER CONFIG), ELAC2 is written within the INOP SYS table to confirm what happens when the aircraft goes into the emergency electric configuration.