Are IM fellowships worth it?

I have always thought fellowship to be a worthwhile investment. You spend a few more years not earning as much money as you could to have your scope can be more specialized towards your interests and ensure you have a higher pay than you would without fellowships.

Looking over these average salary reports, I find myself surprised that to see that the salary of some of these subspecialties to be the same or less than IM without subspecialty. My interests are more directed towards nephro, endo, ID, or Heme/Onc. I hope to be a good applicant in the future to be competitive for fellowships like these, but am wondering if it’s worth it. My hope would be that in pursuing fellowship I’ll either ensure increased pay, or at least better hours.

Of course, me pursuing fellowship is also to ensure that I practice in a field that I love, but I also have a family to think about and every professional and academic decision I make, I do with them in mind.

So, is it a fluke that average salary for some IM subspecialties is equal or less than IM? If not, why do people pursue them? (Not asking for judgement, but to understand and see if that reasoning would be one that would sway me towards pursuing fellowship regardless of salary)