Because the outfield has been arguably the least productive in the majors the past two seasons. Seriously. It's been a sinkhole. And outfield is usually where the offense comes from -- not always glovework being part of the equation. Teams need offense from the outfield. Look no further than the fact that the Cardinals were the only team in baseball that batted their outfielders 7-8-9 to start the year. What's that say, given the gripe you have mentioned?
The numbers on the outfield are telling:
Here is the MLB average slash line for OF from 2019-2020
.255/.328/.444 and a .772 OPS.
Here is the Cardinals
.236/.325/.412 and a .737 OPS
They rank 23rd in the majors in OPS in that time, 24th in slugging. They are significantly below average from a position of important production. They play in a pitcher-friendly ballpark, yes, and that explains some of the numbers, for sure, and it adds context to the fact that they hit fewer than 100 homers and were the only team other than the Marlins to get more than 600 Ks from the outfield and fewer than 100 homers. Out in left field, where it's not common to put a glove-first defender, the Cardinals have had a slash line of .209/.283/.393 for a .676 average. Would accept that at shortstop?
Sorry, that's where the renaissance has to take place if the offense is going to get better.