P5 downsizing and converting 4K. Why?

Pond 5, Adobe, SS converting MP4 and Prores clips to H264 while downsizing them to HD. Any ideas why they do not keep same codec? In another thread Mizamook advised somebody: "Use ProResHQ. h.264/265 is lossy garbage, no matter what". So, why agencies making "lossy garbage" from our high cost and time consuming footage?

It's true I did say that thing. And on a certain level it's still true. But, I now upload only h.264, while keeping my ProResHQ "masters" to hand. I will always do at least that. But I've seen several agencies specify that they PREFER h.264. Easier to store, eh? And the stuff I'm making now is visually lossless for real ... even to me ... at magnifications of 400% and up ... which is ludicrous. Resolve 16 for me played a big part. In reality, the rare occurrence where a buyer will mind, they will ask.

I was just starting to upload in Prores 422, maybe it's not worth and stick to PJPEG.