Drinking the Koolaid?
Why would anyone rely on GTK3 when those behind it take weird decisions, such as removing menu icons and mnemonics? And why? Because... it is not cool enough for them? Because you don't have that on most phone apps, you should not have that on a "desktop app"? (app: crappy and embarrassing piece of software)
I heard over the years lots of rant against GTK3 and praise for Qt5 (because it seems it allows people to do what the f*** they want to do, without being judgemental).