It looks like this is a limitation of the chrome engine, if you scroll down the page, there will be a list of "Problems Detected for Hardware GPU".
Hardware video decode is only supported in win7+: 159458
Disabled Features: accelerated_video_decode
Disable GPU on all Windows versions prior to and including Vista: 315199
Disabled Features: flash_stage3d, gpu_compositing, gpu_rasterization, flash3d, metal, accelerated_webgl2, accelerated_2d_canvas, protected_video_decode, oop_rasterization, accelerated_video_decode, android_surface_control, accelerated_webgl, flash_stage3d_baseline
GPU rasterization should only be enabled on NVIDIA and Intel and AMD RX-R2 GPUs with DX11+ or any GPU using ANGLE's GL backend.: 643850
Disabled Features: gpu_rasterization
Disable use of D3D11/WebGL2 on Windows Vista and lower
Disabled Features: accelerated_webgl2
Protected video decoding with swap chain is for Windows and Intel only
Disabled Features: protected_video_decode
Some drivers are unable to reset the D3D device in the GPU process sandbox
Applied Workarounds: exit_on_context_lost
Disable use of Direct3D 11 on Windows Vista and lower
Applied Workarounds: disable_d3d11