Please see
Domestic Same Day Confirmed Flight Change / SDFC / SDC / CFC / "Standby". Domestic SDFC includes Canada, Caribbean, Hawaii, Puerto Rico, US Virgin Islands).
and
International Same Day Flight Change / SDFC / SDC / CDC (consolidated) (JFK-LHR only).
AA lists SDFC
here. It specifies under which conditions SDFC is offered; when the desired changes do not fit the stated conditions, SDFC is
not available (e.g. on international flights other than to
U.S., Puerto Rico and the U.S. Virgin Islands, Canada and the Caribbean or between / through New York (JFK) and London Heathrow (LHR). (All other origins, destinations / flights are excluded.)
The OP is ineligible for SDFC, and apparently purchased a restricted fare. And probably didn’t bother reading the detailed fare rules when presented with the opportunity.
We may not like the various restrictions, having to read the detailed fare rules or paying more for unrestricted fares, but it’s doubtful the airline - any airline - will waive the rules they have in place merely because we want them to.