I think what's made the Windies suddenly fall since the 1st test match has been the lack of faith from the management in their own batsmen. Ever since the series has started, there has been so much pressure on the top order by both the Windies captain and their management and it seems like that has resulted in an overconfidence in their bowling attack with Holder's decision to bowl first in all three test matches. Yes, you could defend their choice with slightly overcast conditions and some moisture in the pitch, but the Windies bowling attack would be fatigued with back to back matches with a short break in between and it wouldn't have hurt to believe in their batsmen to grit it out and see off the first hour in tough conditions, the way Sibley and Stokes did in the 2nd test match, and Burns two days ago. The Windies batsmen have been under the pump with pressure placed on them from the get-go. Perhaps it could have helped the Windies to have their bowlers rest for another innings at the start of a Test match and be fresh to bowl in the 2nd and 4th innings.
Despite that argument, the Windies batsmen have been unable to build on collectively as a batting group and they missed out on making hundreds and posting big scores which could have seriously put them ahead in the last two games. John Campbell and Shai Hope have been a big disappointment, Campbell doesn't look suited to grit it out against the new ball and he's played poor strokes this series. Hope has no credible scores in Test cricket over the last 2-3 years, while his white ball career has taken off he has looked tentative against the swinging cherry and a few domestic matches should help him polish his red ball game.