its not rare if you ask me.. you can easily get them . ( i agree that you cant expect them same level of clarity and fps compared to original blue-ray disks*)
but then again its waaaaaay better to watch 2160p 10 bit HDR h265 files than watching 1080p 10bit files , yes and its very noticeable
*( you cant archive the same 4K blue-ray disk quality in movies with 4K digital rips unless someone actually crack the security code and rip them lossless)
also if you DM me , ill send you a link to get really good 4K rips of movies for around 2-5GB avg . Fyi you can hardly notice the difference when you are side by side watching the original blue-ray disk on your tv and the digital copy on your phone. ( because i did that test with the original blue-ray -jumanji disk and the ripped copy on my phone )