it's just the first Captains on the fleet are now rapidly approaching retirement, the first F/Os on it are all getting their commands on the 737, the fleet expands by 1 this year, 1 next year and another in 2018, and the lifestyle doesn't suit everyone, those with young famillies appreciate being home every night, and currently, the 787 is ONLY based at MAN and LGW so if you are not based at those 2 bases, you will not get on it. And believe me, we have tried, but the Co only want 787 pilots based at MAN and LGW.
I don't believe it's a negative lifestyle (my own personal opinion), it's not that people are leaving it in droves, just a requirement for more pilots!!!!