I agree 100%, I'm an old-timer and remember to going to the ball games as a kid. The 7th inning stretch was a fun part of the game. It's authentic and could be put in the game so easily. I understand some people don't want to take 60 seconds to listen to the BASEBALL song but there could be an option to skip it. Just like you can skip the intro, I think it should be in the game and have been asking for it for years on their forums.
It's nice they have add a lot of the true stadium sounds and little things that are unique to different stadiums but why they don't include this is beyond me. Maybe it's a "rights to the song issue" or something silly driven by money.
I just wish they'd add it. I've tried in the past to add it as a custom song but the problem is you need a "trigger point" and mid 7th isn't a trigger point like a Home Run or Strikeout....oh well.