I promise I'm not singling you out in this thread.
But, I'm about the same age as you, have been in my industry even longer, and there's a few situations where I would.
1) the new responsibilities are more interesting than my old ones, so I'm making the same money, but am enjoying what I do more.
2) the new responsibilities may not get me paid more in my current job, but allow me to add experience to my resume that will allow me to move into a new job somewhere else either making more money, or doing work that I find more interesting
3) way less likely, but I have reason to believe that the additional responsibilities will translate into more pay or better opportunities down the road at my current employer.
I'm something like 18 years into my career in my industry, and I've generally tried to take as much responsibility as people will give me, with the expectation that over time the money will follow. For the most part it has.
Can confirm I’ve done all of those and it’s worked out well. But I still had to move cities and eventually employers to get any of my hours that I put in to improve rewarded.
I’m not advocating for not working hard. I’m just saying people need to out themselves first and actively seek out ways to cash in their time and energy.
When it comes to compensation one’s current employer is often like a lazy partner, they feel like they already got you so they don’t need to try anymore.