On a lot of budget airlines there is not enough room to get into a suitable brace position.
And there is the reality, also by 'normal' airlines if one is larger than average in height. Yes the seat in front will tip forward, but still the standard brace position is hard to achieve outside of first/business/exit row seats. Take into account the many rotund passengers, even if just in the belly area and it gets more problematic to brace.
SHJ