You can't keep burning out the bullpen, which the Angels have done a lot of (126.2 IP, 2nd most in baseball behind the Padres--but at least with the Padres, it's due to rebuilding.) Plus, the Angels rotation has significant injury risk, with all of Skaggs, Richards, Heaney, Shoemaker and Tropeano having spent significant time on the DL in the last year or two due to significant elbow/shoulder injuries, and in Shoemaker's case, his skull. And Bridwell, a call-up option, is also hurt. And Jaime Barria is not close to MLB ready--especially after that disaster in San Fran. And the lack of innings from the rotation (139.2 IP or 4.8 innings/start, worst in baseball), is a serious issue.
And the offense stinks. Outside of Trout, there isn't much there--part of the reason Showalter decided to walk him basically every time yesterday, and it's shown the last 2 weeks, as they've gone 4-9 since their 13-3 start, with the lack of offense the main blame. That 17-12 record is an illusion--the pyth record is closer to .500 and out of contention, rather than being a top team in the West.
Getting on base? They don't have it--near the bottom of the AL in walks and OBP. And their average is middle of the pack--mostly due to Trout and Simmons.