Depends on how the companies you prefer allocate rewards and whether you are building your career across or within companies.
The primary benefit of learning the domain is increased productivity. Problem is, plenty of businesses place virtually no value on productivity because it is hard to measure. Or if they do measure it, they do it in a way that makes productivity seem high but with terrible results, so the gains come from gaming the measurement rather than true understanding. Budgets are very easy to measure.
The average business would immediately notice an extra few cents in salary costs but probably would not notice a proportional drop in productivity. Plenty do not notice massive fall-offs in productivity or if they do, don't really understand what it is well enough to take concrete action on it.
I suspect that most office workers could allocate one day every two weeks to do next to no work and instead do some kind of freelancing or build out a startup. That is a 10% hit to your productivity. Most office workers could get away with this and I know many that do. I know some who allocate one day a week to this. That is theoretically a 20% hit to productivity.
Could any of those people get 10% or 20% raises? Not a chance.
So in the average business, no, simply because they don't care about productivity enough to measure it and thus they can't reward it. This is especially true if your main path for career growth is outside the company. Inside the company, it can be used to make a solid case for promotion, but the average person gets their promotion from moving.
There are certainly companies where it would be rewarded, but you would see that in high levels of retention as well as structured development programs. If a company valued domain knowledge, it would be quite evident.
This is a human thing. Customers will revolt if the price of an item increases. Cut the amount of stuff in the same package and few are the wiser.