The system partition is made some fixed size, the same way disk partitioning works on PCs, and never resized, because resizing file systems is still a non-trivial task. It often has some free space too to accommodate future system updates.
On my 128 GB Pixel 9 Pro, /data is 109 GB. The rest is /system (although `df -h` doesn't show it explicitly, no idea what's up with that) and various other system-related partitions.
If people are paying for upgrades to storage space it's completely reasonable for them to be annoyed by bloatware