In the US maybe, but given that they're a remote company with people all over the world, they don't necessarily have to live by US standard (especially when it comes to spending!).
40k USD is a VERY good developer salary in Argentina, and I'd bet that in other countries a lower figure might make the cut too. I can definitely understand why they'd hesitate to pay thrice that amount.
I believe it's over 5 times the average salary.
And its not just me, they've done this in the past as well: https://news.ycombinator.com/item?id=10924957
Also when you work for a remote company, they are cutting cost in terms of office and all which should reflect back in the salaries, the whole idea of working remotely was to mutually benefit both the employeer and employee and not just gitlab using their whole startup argument to cop out when they want on that "truly remote" so-called transparent company.
I fail to see how this disproves it, it merely proves that you're not a good choice for them (because you live in a, relatively, expensive region).
This argument sounds more selfish than fair to me.
A company should follow some rules to neutralise the discrimination between employees, it shouldn't be all pick and choose and take advantage where they can, that's not really the reason one should have a remote distributed team to get cheap labor.
If what OP is saying is true, then the company might as well be upfront about it.
Regardless of that, the average salaries are posted online and they seem to suggest quite the opposite to what they offer people outside of US. It's just an indication of how much of a bully culture they have in negotiations or discriminatory, they might as well just outsource the site and not have a team of their own at all.