Dear,
They are default values.
You may increase them if you want. In OPPQ, this is the number of max. proposals per date.
"If this field is left blank, an unlimited number of order proposals can be created per date."
Kindly check:
https://scn.sap.com/message/6959976
https://scn.sap.com/thread/1674219
Best Regards,
Rajen