For employees of the game industry, aren't standardized engines a net positive?
I can't think of many things worse in software development than "I'm an expert on my employer's obscure, only-used-here system."
Your employer knows you can't work anywhere else, and assuming they don't shoot themselves in the foot by allowing one person to become mission critical, they've definitely got the power in negotiations.
This is a fairly nuanced question so I'll try to explain some of the reasoning.
Unreal Engine is standard in so far as studios use it as a base in developing their own game, where they end up creating a fork because they need to adapt or more often replace entire systems. So in the end each studio ends up with their own non-standard fork of the engine, branched from a specific revision, and merging the latest changes from upstream will be at least a month long endevour. This is what I know from personal experience and from interviewing at about a dozen studios last year.
With this you get a slightly different version of the engine and tools at each studio, and it affects disciplines differently. For some creatives it ends up being the same at every studio because the tools they interact with remain largely unchanged, for others they end up using custom built tools at each studio. Likewise some programmers are fine just using the engine and developing systems on top, but others are not and it drives a lot of skilled people away.
So as an employee it is a double edged sword, on the one hand there's at least some standardisation where you are at least familiar with the tools and engine used in the new studio you're joining, but on the other hand you're now one in tens-of-thousands and much more of a replacable cog.
That is one of the supposed selling points of Unreal Engine to studios - that they can hire staff more easily - but if every studio uses the same engine then it's not a benefit. It also means that some skilled people won't want to join the studio, as they don't want to rewrite systems or be a code-janitor, and I've heard many people leaving studios because they switched to Unreal.
I can't think of many things worse in software development than "I'm an expert on my employer's obscure, only-used-here system."
Your employer knows you can't work anywhere else, and assuming they don't shoot themselves in the foot by allowing one person to become mission critical, they've definitely got the power in negotiations.