All modern videocards support fast video-decode. Premiere is not using this free bonus.

We and many users experience sloppy 4K ans 8K performance in source window with dropping frames and hight CPU utlilization as a result.

The new Nvidia RTX2060 RTX 2070 and RTX2080 even support 10 bits video decoding. See decode matrix form Nvidia.

Even the fastest CPU will have problems some videostreams, even 4K 10 bit drops frames not to speak of 8K. With hardware decoding this is no longer a problem. The CPU utilization will be lower and the Premiere will be more responsive as a result.

For a lot of users working with h.264 or h.265 this will be a big performance booster.

As an example, look at the free videoplayer VLC. It plays all formats 4K without high CPU utilization. If they can do it, why not Premieren?