Why is there no netting along the stands in (many) US baseball stadiums?

The freak accident at Fenway Park, last Friday, where a 44-year old woman was hit by a broken bat, makes me wonder why there is no netting in many of the US baseball stadiums. I must admit that I have been to only three MLB stadiums and three MiLB stadiums so far, but nowhere, except for the backstop, there was netting to be seen.
In Fenway Park they warn the fans with warning signs like this.
Of course a bat hurts. Duh!. I realize that fans should pay attention to the game when someone is at bat. But even then there is a risk of being hit by a bat or foul ball. So why no netting? In the Netherlands there is netting along the stands in two of the three baseball stadiums we have. Of course it is annoying at times when you want to take a picture, when the camera focuses on the net instead of the players.

Up here there is a photo of the Neptunus familiestadion in Rotterdam. As you can see there is netting in front of the stands.
So is in the Pim Mulier stadium in Haarlem.

Like I said, it can be annoying. But what do you prefer? An “obstructed” view or a baseball or a bat against your head?

I am pretty sure that there are fans with a complete different opinion, but I think the MLB and MiLB clubs have to protect their fans, so netting should be placed along the stands.