Why didn't they use their powers to get rich?

Well that's the thing; these people tend to be really stupid. The most common thing they do is go out in public, often without a mask, and pull off a major heist. Even if they do have a costume that disguises their face, their costumes sometimes don't include proper gloves so they're bound to leave fingerprints, (I've seen these fictional thieves with finger-less gloves more times than I can recall) their head gear can leave their hair exposed so they can very easily end up leaving strands of their hair behind, or they don't disguise their voice as Andrew failed to do. They also have a habit of bumbling things up and getting hurt; either resulting in them being captured while unconscious (again, like Andrew) or their DNA getting left at the scene.

Sure, those are tropes that writers and artists typically depict for creative purposes. Costumes, for example, are rarely designed based on real world functionality and instead tend to be put together based purely (or mostly) on aesthetics (finger-less gloves hearken a tough biker look and having, say, long, blond hair flow out of a mask tends to be a look that artists enjoy depicting). However, they do have the excuse that real world thieves make stupid mistakes like that all the time. So, when you see a character not trying to get rich before their powers go away and you think they're an idiot as a result, it's probably for the best that they don't try to make money as they are idiots and will screw up.

When talking about just yourself, sure, you can make the case that you'd be much smarter if you were in their place, in part, because you have seen their mistakes and therefore know what not to do. But, as you yourself pointed out, it's hard in this day and age. Not just with cameras all over the place, (including people with cell phones) but with how advanced forensic have become and all that. You really have to keep in mind a lot of things that would give you away and, while it's easy to think you can do that while sitting on a couch and laughing at how stupid characters are for making those mistakes, it's not so easy when you're actually in the thick of things, with your heart pumping and time on the clock. Throw in a few unknowns (like the cops or another person with superpowers suddenly being involved) and the chances of you messing up increase. Hell, your powers can go wonky on you in the act - If you know so little about them that you're afraid of losing them before you had a chance to get rich, there's certainly the risk that they can give you problems at any moment.

Also, again, you say you'll only tell people who you trust, but the second you tell anyone, you're at risk of it all falling apart on you. Criminals, very commonly, get turned in by people they thought they could trust - Parents have turned in their kids and life long friendships have ended over things like this. Unless the power you get is the ability to read minds, you never know what anyone is thinking, no matter how well you know them.

Jealousy, for example, would be a big motivator. Why do you have all this power and all this money when they don't? Sure, you may be sharing some money with them, but you still have so much more and what happens if they ask you for more and you think you've given them enough (especially if your powers are gone by this point and you want to save what you have)? Something like that can ruin a friendship, especially if there's the perception that you changed as a result of your new found power and wealth. Then, someone can rationalize their betrayal by saying to themselves that you deserved it. Maybe you know better people than I have, but based on my own experiences and the things I've read, (in regards to how criminals get caught) I wouldn't be trusting of anyone with something like that.