I think you will find its because most people have probably taken the seats already. The time to book was when the schedules were loaded, not now after the announcement. I've spent the last few months booking all my 2022 and pretty much been able to get the exact dates and class I wanted on usually very in demand routes such as to LAX and LHR. When the schedules were loaded over the last few months, there was amazing availability but I've been watching it be snapped up over the last couple months as confidence resumes.
Overall though I think its been pretty good. Just yesterday I was able to snag SYD > LAX in J on QF in May on the exact date I wanted, that was pure luck though, I was on the phone to a QF agent when the EF alert came through and I was able to book it immediately.
Check JAL, been seeing plenty of availability with them.
As new flights are loaded as demand slowly picks up I think you should see availability increase. I think you need to keep an eye on when the new flights/ routes/ airlines/ aircraft upgrades (777 to a380) are loaded and that's when a wave of availability shows up. Good luck!