The guide isnt saying 95% of source content is h264. Its saying 95% of files you would download when pirating are h264. The scene, by and large, is transcoding h265 4k to h264 720/1080. The 4k h265 is available but its considered the 'premium' option.
Most 1080p encodes I see on pirate bay are h.265 these days.
But frankly, most of what "the scene" produces it trash. I gave up on waiting for proper blu-rays for the remaining seasons of Bojack Horseman and pirated them a few weeks ago, and all the options were compromised. The best visual quality came from a set that was h.265 encoded with a reasonable average bitrate, yet the quality still did not reflect the bitrate at all, with obvious artifacting in fades and scenes with lots of motion. I usually get much better results at only slightly larger file sizes with my own blu-ray rips.
I'm pretty sure the key difference is that I go for a variable bitrate with a constant quality, whereas most scene groups want to hit an arbitrary file size for every episode regardless of whether or not that is feasible for the content. Every episode in this set is almost exactly 266 MB, whereas similar shows that I rip will vary anywhere from 200 to 350 MB per episode.
Yeah, tv shows are tough. I should caveat that I'm talking mostly about movies. I find a _lot_ more 265 content for tv shows. I also am generally on usenet rather than torrenting.