Yep.Tinybuild Games (an Indie dev) lost almost $1 Million because of that.
Well, you guys are a bit off on a couple of things. By "almost a million" you mean less than half a million, it was $450k worth of keys stolen from a market place they tried to run on their own with zero key security, and by developer you mean a publisher of over 30 games who, developed a single game of their own. It doesn't make it a good thing of course, but it's important that we talk about the facts so that people aren't working with hyperbolic truths.
Telling people not to use G2A doesn't solve a problem - they could be completely removed from existence you can bet that people still would have still stolen them, the doors were wide open for them to do so and it came at zero cost to themselves, and there will ALWAYS be a market for second hand keys, and like it or not people are well within their rights to use it and G2A does their legal requirement and deletes thieves and refunds victims. I say these facts because whether you feel that's morally or ethically good enough doesn't change the fact that you can't and won't be able to just shut it down. If you want to see a change, or improvement, to the state of the key resell market you aren't going to get there by doing this, the end game result that you are pushing for is that nobody uses their right as consumer, so as a result the people who steal keys say, oh well I guess there's no point in stealing these keys at zero cost to myself, and this just isn't a practical plan to the future going to happen.
Key reselling exists at the state it does because the industry has weighed the loss of profits as far less impactful than actual acknowledging and supporting people's rights to resell digital goods. There's a reason Steam is as big as it is, and a reason people are buying these keys instead of just pirating them at all - people WANT to pay for their games, and nobody buys a key WANTING to go through the potential drama of a stolen product. So don't think for a second that Steam or someone else couldn't take complete control of the market by officially supporting it and integrating it with their products, people would use that over G2A in an instant. The industry is trying to double dip, by doing zero to support or acknowledge the fact that customers have a right to resale on their products, its something the industry has been lagging behind heavily on and skirting for a long time, but at the same time driving a narrative trying to discourage people from using resale markets.
If you want a change the realistic ways to do it is push for Steam and/or similar people with the power to do so, to create a market with monitoring on the keys for their services. I will continue putting my dollar into the resale market and support consumers rights until it gets supported. If that's not good enough, the next best thing is for devs not to create market places where people can just come through and fraud them out of $450k worth of keys that they can't keep secure, just so they can avoid paying Steam their cut. If you feel Steam's cut is too unfair, than push for changes to that, or support their competitors and encourage others to do the same. The angle you guys are going for is just the wrong one, and reeks of industry driven bullshit + appeals to a false moral high ground. They have the power to change this but you guys are pushing at the people who don't.
Just a different perspective for you guys. No ill will for you guys for feeling the way you do because I know it comes from a well-intentioned place - I just don't believe it's a fair assessment.