Sendcmd in ffmpeg

Why sendcmd in ffmpeg works with drawtext, but does not work with scale, rotation and other filters?

Example (this code works)

ffmpeg -i testIN.mp4 -filter_complex "[0:v]sendcmd=f=testTXT.cmd,drawtext=fontfile=PF.ttf:text='': fontcolor=white:fontsize=150" testOUT.mp4

testTXT.cmd

0 drawtext reinit 'text=111';
1 drawtext reinit 'text=222';
2 drawtext reinit 'text=333';

Example (this code does not work)

ffmpeg -i testIN.mp4 -filter_complex "[0:v]sendcmd=f=testTXT.cmd,drawbox=x=10:y=10:w=100:h=100" testOUT.mp4

testTXT.cmd

0 drawbox reinit 'x=20:y=20:w=200:h=200';
1 drawbox reinit 'x=30:y=30:w=300:h=300';
2 drawbox reinit 'x=40:y=40:w=400:h=400';