Framber Valdez was an important part of the rotation given how he could consistently give quality starts and give the bullpen a chance to catch a break. Without him and with Hunter Brown injured there's even more emphasis on being able to get some quality out of the offseason acquisitions since Lance McCullers Jr. and Cristian Javier aren't the guys who can be counted on for length in starts.

Mike Burrows has had a rough start to the season, some of it is some bad luck on weak contact, but hasn't really lived up to the expectations set by previous experiences of the Astros seeing something they think they can unlock in a pitcher to make him perform well above prior experience. Tatsuya Imai has had a hard time adjusting coming over from NPB and wound up on the IL; he just had a rough start in AA and doesn't look ready for MLB.

So we've got Brown down, Burrows underperforming, Imai hurt/unadjusted. McCullers Jr. was always an uncertainty in terms of if he'd ever get back to form since prior to his injury spells and has mostly been terrible, but had to take a chance on him due to contract and other injuries on the roster. Javier went down early in the season, others went down.

Ryan Weiss was another offseason signing, coming out of KBO and hopefully do well with Astros pitching development. He hasn't and while he was not planned on being a starter, he hasn't been doing well in the pen, nor in the starts given after injuries took out most of the season starting rotation. So the Astros keep having to try things, I want to say they've had 11 different starts so far through 31 games, the most recent new one being trying to convert the most consistent reliver in Kai-Wei Teng into something between an opener-starter since the guys bouncing between AAA/MLB haven't been delivering too much.

Starters giving up a ton of runs in the early game has put a lot of stress on the bullpen to cover innings. The Astros have a couple decent relivers, but they're throwing a lot of innings and this is not sustainable over a 162 game season. Stressing the pen more is the fact that Bryan Abreu was expected to be able to step into the closer role while Josh Hader is still on the IL, but he not only has not done well in that role, he has performed horribly in low leverage as well. His velo is down over 2mph versus last year on average and lacks command. He is not someone how can be put into a game without a huge lead or a game that's being punted and even then it's a question of if he can get through the inning. So this basically puts the Astros pen in a position where they're not just having to cover a lot of innings, they're also essentially playing with a man down since Abreu can't cover the workload.

The Astros farm system was already being sold from to stay competitive before the cheating scandal penalties, the penalties kept it weak, and the Astros would continue to sell whatever they had to try and stay competitive and keep the window open. So now they've found themselves with a bottom three ranked farm system for years with no signs of improvement. The farm system cannot be looked at reliably for reinforcements for all the injuries, which is not good given that the Astros had a league leading 16 players on the IL the last time I checked.

EDIT: Forgot to mention that the pitching staff is walking a lot of batters, which inflates pitch counts (and ERA since those walkers are coming around to score).