Very sad. Opus Magnum is definitely the one I played the most. GOG, don't you dare mess around and reject this!

Well...according to SteamSpy he has sold 3.072.000 games at an average price of $10.33

Even if we take the lowest price (apart from "free") of $1.49 as the multiplicator for all these games, he still made $4.6 million (pre-taxes).
I would love to have that kind of money on the bank.

And if we're going with the average of $10.33 as the multiplicator...we are at a whopping $31.7 million (pre taxes).
I don't think he needs to work anymore.

Zachtronics has been around for 11 years as a commercial endeavor starting with Spacechem. So Lets take $31.7 million and cut it down to $2.88 million per year. Steam sets the standard of taking a 30% cut and I dont see any reason that Zachtronics is getting any deal better than the standard. So already down to $2.016 million after the storefront cut.

Some of that revenue has to go towards salaries. I recall reading a Gamasutra article (I think this was back in 2011 or so) that did some back of the envelope calculations and decided $1 million dollars was enough for one year's salaries for an average team of six people. That's about the size of the Zachtronics team so already half of the post-storefront revenue is going just to pay salaries.

That is just salaries. So that last million per year has to cover everything else. All the equipment that a company needs. Any leases/rentals for office space. All applicable taxes. Post-game tech support might need some funding, too. And then Zachtronics parent company Alliance Media Holdings wants their cut.

So even if we take $31.7 million pre-tax revenue as true, it still isn't much by the time everybody takes their slice of the pie.

It's still easily enough that everyone involved was making decent money. (And I doubt there's renting office space or stuff like that since it's highly likely this is several people working together remotely, which is typical.) Again, this was never about "have to get a full-time job" or anything. Just time to do something else.

There's also PR and advertising costs to get the attention on the games to start out.

there are also economic security. Barth have previously stated that the job he has now is his first full time employment, and that he have had it for a year, but found it difficult to do full time game development and full time work. yes, he might enjoy game development more, but is he married? does he have kids? do he need to think about college funds? making sure the mortgage is paied each month? having a pension when retiering?

Game development is quite fickle, and you more or less live from game to game if you are a full time indie developer, which is why most have a full/part time job and do games on the side. if you have commitments, then i can understand why you would go for the more secure (though pershaps the more 'boring') option
to be fair, Zachtronics never have much PR / Advertisment. They had a core group of very lojal fans (/wave) and the news of the games spread by word of mouth. when they got 'famous' for the games they made, then the game press laos made interviews and reviews od the games as well, which Zachtronis did not need to pay for. I do not remember seeing any specific advert for any of their games, apart from the teasers they made themselves for their own website, which were also used everywhere else as well.

I don't know how SteamSpy do the calculation but I guess the raw 3M number include keys bought in other places, including bundles, like 1€ Humble Bundle.
Again, I don't know how those 3rd party keys share work but if any Zach game is included in giveaways, 1€ Humble Bundle or even as a indie package that was given to all costumers, 3M start to not look as impressive.

But hey, 3M Steam copies is not shabby at all for some "niche" games.

While his more complex games are definitely not for me, it'll still be a shame that he won't be making any more. Definitely one of the more notable and unique game makers.

There's other types of PR like the kind with fake fans on forums and shills on youtube channels or paid for "news" articles on websites.