Not sure that 'playing scared' is the right term.
More objectively, the Steelers play 'conservative' football for sure and said style does bite them in the arse more often than not.
On one hand, this 'keeps them in' every game and usually avoids blowout losses. However, on the other it keeps them from definitively beating their opponents, too.
Overall, it is frustrating and appears to be a fixable 'problem'.
EDIT: That was a horribly dyslexic attempt at spelling 'definitively'.