Houston's bullpen got torched when it counted
Bullpens have outsized importance in the playoffs as teams are much more aggressive in pulling starters at the first sign of trouble. This should have been relatively good news for the Astros as their bullpen had the sixth best bullpen ERA in all of baseball in 2023. However, some troubling peripherals and a lack of usage meant that they ranked just 18th overall in fWAR this season and that proved to problematic in the ALCS.
Make no mistake about it: the Astros bullpen was simply not good enough against the Rangers. They gave up eight runs in Game Seven alone and that was after giving up five runs in Game Six and struggling in Game Three as well.
Part of the problem may have been that the bullpen was not used to be used this much this season as the Astros' bullpen had the second least innings pitched in 2023. One would think that that would have meant that they were well-rested for the postseason, but Houston's relievers had to play a LOT in the ALCS and they certainly looked like a group that was pretty wiped by the last two games of the series.
Again, Texas played their part in this as well. The Rangers continued to refine their approach and make adjustments to Houston's gameplan which paid off for them as the ALCS progressed. Great teams make plays when it matters and unfortunately, the Rangers did while the Astros failed to close the deal.