av1 getting worse results than hevc (h265)

[abcjme]

I converted an avc (h264) file to an hevc (h265) file and an av1 file.

Relative to the hevc (h265) file, the av1 file is far larger in size, and the av1 file has worse psnr and ssim results too.

With the hevc (h265) file, i used the default crf setting (28)

av1 doesn't have a default crf amount, but i used the ffmpeg recommendation of 30

Here's the command i used to do the hevc (h265) conversion

C:\Users\l\Desktop\6-app\ffmpeg -i y.mp4 -c:v libx265 -preset 8 -vf scale=1920:1080 -r 60 -ab 192k -ar 48k -map_chapters -1 -map_metadata -1 z.mp4

Here's the command i used to do the av1 conversion

C:\Users\l\Desktop\6-app\ffmpeg -i y.mp4 -c:v libaom-av1 -crf 30 -b:v 0 -strict experimental -vf scale=1920:1080 -r 60 -ab 192k -ar 48k -map_chapters -1 -map_metadata -1 z.mkv

Here are the psnr and ssim results of the hevc (h265) file

ssim

Y:0.981764 (17.390662)
U:0.992258 (21.111573)
V:0.992246 (21.104816)
All:0.985260 (18.315015)

psnr

y:41.620801
u:48.257839
v:47.699066
average:42.905441
min:38.873493
max:58.862531

Here are the psnr and ssim results of the av1 file

ssim

Y:0.923286 (11.151250)
U:0.991684 (20.800862)
V:0.987425 (19.004970)
All:0.945376 (12.626126)

psnr

y:27.332443
u:44.955360
v:41.569108
average:29.034062
min:8.783696
max:59.518112

Here are the size results of the files

avc

3.9 mb

hevc (h265)

4.6 mb

av1

9.59 mb

I know i'm compressing an already well-compressed file, I didn't necessarily expect a smaller file size - but i did expect av1 to outperform hevc (h265))

Here are the actual files

https://www.dropbox.com/s/4xy7tsys5cswngb/combo-3-avc-original.mp4

https://www.dropbox.com/s/fnakxv248sz8w9w/combo-3-hevc.mp4

https://www.dropbox.com/s/07x5ddc54jn7xzb/combo-3-av1.mkv

Why would such poor results occur?