Because it's meant for editing, to be able to cut anywhere without re-encoding. So it needs to be all I-frames.

And you're going to use a very high bitrate.

This is way more space than consumer codecs use. But still way less than uncompressed video.

I’m struggling to imagine a use case for removing bits of a video and then saving that intermediate back out without editing or reencoding but if that’s what a video editing workflow calls for then fair play!

you just described pretty much every single modern day video capture. pretty much all of the dslr/mirrorless cameras are capturing a higher bitrate h.264 as source.

How would you edit a sports highlights package?

shudder, uncompressed. i have nightmares of v210

H.265/h.265 make use of IPB frames. The P and B frames refer back to the I-frame so that each P/B frame has much less information than the I. So if you use only I-frames, that's the best that codec can offer, at a decent bit rate. there's much better descriptions on the web.

That doesn’t make sense, at the same bitrate encoding frames with no dependency on previous frames can’t possibly look better or be the best the codec can offer, or there would be no reason for other frame types to exist

They didn't say "same" bitrate but rather "decent" which I take to mean "sufficient" -- and obviously much larger than what you get with lossy(er?) params