H.265/HEVC takes about ten times as much computation to encode than H.264 [1], so H.264 still has legitimate technical use cases, even with licensing/patents aside.

This makes it great for a company like Netflix or YouTube, but less good for one-to-one and/or battery sensitive use cases like video calls. However, specialized chips help, and some mobile devices can record in HEVC in real time (mine from 2019 can). I believe current smartphones have HEVC encoding hardware, but I'm struggling to find a source for that right now.

I haven't seen the details of this new codec yet, but it's quite possible it also has a large encoding cost which will make it better suited to particular use cases, as opposed to a blanket upgrade.

[1] http://www.praim.com/en/news/advanced-protocols-h264-vs-h265...