Anything Qt might never really have been an option?
Maybe GTK is seen as a better guarantee for 'Purism'. A - let me say – GNU/Linux sensitivity which could well be more outspoken in the US of A than in the Old World.

Talking about differing sensitivities.
Just look at what happened at Jolla('s management) during their last trek through the Valley of Death. Most (Finns) stayed on. Not being fully imbued by all aspects Finnish, Marc Dillon, Cybette, ... left.
Did they sense a Big Bear backed rescue somewhat differently?

PureOS, Librem …Claims that don’t come cheaply.
Purism is even less a (normal) company than Jolla (or Canonical). Where Jolla says (basically) no to Android, Purism says no to Qt as well. For sure, having a couple of (more than simply) successful crowdfunds helps when going their long own Librem 5 way.

Finally. What genuine out-of-the-box(!) smartphone alternatives does one really have on the Western side of the pond when not opting for Android, iOS, …?
Jolla/Sailfish is not active over there and fails HW-wise on the Eastern Atlantic.