It's indeed sad to see. Game networking techniques have been known for multiple decades and yet still haven't made their into any of the major publicly available engines (notably Unreal and Unity). What gives?
As a game dev of 10+ years myself, I have a few theories:
1. Multiplayer networking is the "secret sauce" that creates moats/barriers to entry for incumbent studios. Think Rocket League or Fortnite or StarCraft 2. The tech exists, it's functionally well understood, but hard to implement at a high level of quality. Why not keep it to yourself? There is more money in holding onto your game revenue monopoly than trying to sell the network tech.
2. Game genres differ greatly in their networking needs. Rollback is great for fighting games but that's about it. StarCraft uses delay based deterministic lockstep. FPS games use (typically) ad-hoc server authoritative state syncs with client side prediction. Other complex games use full determinism with rollback, sending only inputs over the wire. Some cheapo indie games using client authoritative models (open to cheating but easy to implement, arguably fine for coop games). There are even more variants and blended approaches but you get the picture: there is no one size fits all approach and many are mutually exclusive so it's harder to package into an engine as a comprehensive solution.
3. Networking a game properly involves very leaky abstractions. It is impossible to write gameplay code for a networked game without understanding the nuance of the network model. This makes it substantially harder to develop the game, and this hurts the major game engines' marketability, with both major players Unity and Unreal guilty of selling themselves as "look ma no code required" solutions. Similar to point 1, not worth the money to sell this.
I don't see a great way out of this unfortunately. The only good networking middleware I know of is Photon and they're not exactly an easy to use product either. Hopefully we see better open source tooling in the future.