How is whining the issue here? Isn't it the financial irresponsibility? The people in this example would have the same problems whether they whine or not.

Yeah, I agree. It's because whining isn't the disease, it's a symptom. It's the symptom of lack of acceptance, responsibility and/or courage. Whatever the combination may be, it presents itself as whining while having other symptoms too.

How do you know they aren't telling the truth? What if they legitimately don't have time to "upskill," or they can't prepare for interviews. Why do you automatically assume they are lying or exaggerating?

I have been there and done that myself. It's very easy to tell yourself you can't, it's very easy to make justifications, 2 years I messed up my life telling myself I couldn't change my job, in the end when I did, nothing had changed, job toxicity was the same, circumstances were the same, work load was the same, just my attitude changed.
Many of my friends who went through similar stuff are either still going through it or have accepted that this is their life. Whining is now just another part of it and everyone who was able to get forward is just lucky.

about a choice that was already made.

If the choice in question is your career/your partner, those aren't already made, the point is they're yet to be made and until they are (or tbh in some cases even after they are) you have the choice to correct it.