In my experience as a hiring manager, it was a lot easier to find qualified developers than it was SREs or similar. Plenty of people doing ops work, but not a lot of them at the senior level. And the senior ops people we find demanded, rightfully, much higher salaries than the developers.

I've found the opposite to be true. There's lots of mid-level developers around who are capable of handling most common stacks. Even mid-level Ops people are few and far between. Truly senior Ops people are a rarity and in very high demand, even if salaries aren't matched to that demand. The difference in responsibility in those roles that you are entrusting an employee with makes the comparison a bit difficult, but generally speaking far more is expected of Ops hires than Developer hires at most companies. When you hold the keys to the kingdom you have an extraordinary ability to cause damage to the company purely through innocent mistakes, much less malicious behavior.

I think what you're explaining is actually reality (not shown on the salary graph).

There's a large donut hole in ops. The truly high demand people make way more than the salary listed there. However, developers are within the normal range.

I.E. - Developers make more on average, top end Devops pays more.