Trying to realtime encode 4k into AVC using pure software encoders takes about 80 cores/hyperthreads. Then you need to meet the tight 70ns? timings of the SMPTE 2022-6/7 protocols (i.e. 12gbps without using jumbo frames because reasons).

It's also necessary for clip switching. If you want frame accurate clip switching (i.e. show->ad->ad->show) you need consistent and precise pointers into your files.