Pardon my ignorance, I could be wrong, but isn't it because abortion was less accessible (and is now mostly illegal) in Indiana?
Abortion has been banned since 2023 in Indiana (with some exceptions).
The vast majority of the state's 123 baby boxes were installed well before the ban went into effect.
The state I live in is a very 'blue' state, always returns two Democratic senators to Congress, and abortion will never be made illegal here. In fact, many women cross state lines for abortions here since neighbouring states have banned it or restricted access. The state still has lots of baby boxes. They are installed under the private initiative of individual municipalities.
There is one militant/ unhinged website that I am aware of that is devoted to the outlawing of baby boxes on grounds that those who support the boxes are a bunch of rabid pro-lifers who want to get abortion banned everywhere.
Most cities/ towns installing the baby boxes in my state are aware of the number of abandoned babies found in the state's biggest city annually. This city has resisted the boxes for some reason, and the (blue) state law asks that the mother hand over the baby in person, with obvious drawbacks wrt anonymity. Mothers who are in this situation are usually afraid of the news of a baby's birth getting out. There can be very difficult family circumstances, cultural disapproval, etc, and many pregnancies are hidden, with the mothers determined to keep it that way.
Fire departments and police in the US are employed by and paid by individual municipalities, so they have this leeway in an incorporated area (village/town/city) to determine their own approach regardless of the state law. Police and firemen have no desire to find dead babies on their shift.
https://www.fox32chicago.com/news/illinois-indiana-baby-surrender-options