It was already compatible with GPLv3 and BSD licences

I don't think anything was implied about reciprocity. If you're building on a work, you have to go along with the conditions applied to that work. People sometimes make a big deal about how "generous" they are ("I attached as few conditions to my work as possible!"), but that simply isn't the aim of the GPL.

Technically, anyone who wants to build on top of the combination can use whichever GPL-compatible licence they like and wait for someone else to replace the GPL-licensed part under a licence they prefer. Usage of the GPL merely invites people to undertake a common activity within a framework that seeks to uphold specific properties of the resulting work.

There are all sorts of reasons why a project might switch to using more or less permissive licences - they may indicate a change in the way the interests of different groups of people are prioritised by the developers - but given the potential effects of such changes on end-users, I don't see anything wrong in voicing end-user concerns about it.