Why JW 51B was defended differently from PQ 17

Why did the Royal Navy defend JW 51B so differently from convoy PQ 17?

Experience after PQ 17, confidence in the covering force, firmer orders, and aggressive flotilla commanders produced a very different response.

The officers responsible for PQ 17 acted on different information and orders, so the comparison does not reduce the earlier disaster to personal cowardice. By late 1942 the Royal Navy trusted its covering force more and had resolved that the experience would not be repeated. Aggressive destroyer commanders now led several flotillas and treated withdrawal as a last resort. Their earlier service under a small group of hard-driving officers had also created a recognizable command culture.