@janneke such people pursued open source because they wanted another 'new world' to colonize, to create themselves, not because they cared for the principles in play.
They pursued it out of the 'right' that the u.s- and most of the countries who copied it- was founded on; the right to take whatever you can and build whatever you can with it, so long as other powerful people allow you too (keeping in mind at the time 'all men are equal' meant, by their definition of 'man', 'all powerful men are equal'). The tech-colonialists may not realize this, but it is their fundamental ideology, for the same reason so many video games are based on colonialist themes.

Now they feel they've built enough infastructure for their 'new world', and along comes a technology that can fill it with stuff even more quickly. As their reasoning is already based on at-best grey area understandings of boundary and consent, why would they care that this tool is built with stolen work? As they were building this new world with every intention of ignoring the current one, why would they care if its resources are stripped for this tool, as they have been by colonialists for centuries?
As their new world was from base built on dubious grounds of stability- both in resource availability and code stability- and has largly been kept afloat with the work of various individuals and efforts, often donated for free. Why would they feel this next step will be any different?

They have never been provided sufficient counter reasoning or pushback. Only now are they finally running into it, and so only now are they making it obvious what their disagreements are.