In my experience, having a fixit week on the calendar encourages teams to just defer what otherwise could be done relatively easily at first report. ("ah we'll get to it in fixit week"). Sometimes it's a PM justifying putting their feature ahead of product quality, other times it's because a dev thinks they're lining up work for an anticipated new hire's onboarding. It's even hinted at in the article ('All year round, we encourage everyone to tag bugs as “good fixit candidates” as they encounter them.')

My preferred approach is to explicitly plan in 'keep the lights on' capacity into the quarter/sprint/etc in much the same way that oncall/incident handling is budgeted for. With the right guidelines, it gives the air cover for an engineer to justify spending the time to fix it right away and builds a culture of constantly making small tweaks.

That said, I totally resonate with the culture aspect - I think I'd just expand the scope of the week-long event to include enhancements and POCs like a quasi hackathon