Damon said in an interview with the YouTuber Jake Hamilton that an artist wants to add a permanent bronze statue of Williams in the lagoon area of the Garden [in the spot where where they filmed the famous bench scene in Good Will Hunting].
“The idea being that if you feel alone you can go sit next to him, which I think is the coolest idea. It would be like the most beautiful installation and like such a tribute to that guy, who I think would’ve loved that.”
Probably because it already has a lot of memorials and, having been there, does not have a lot of space to add more without turning it from a functional park to an outside museum. There are a lot of historical public spaces in Boston that are unable to function as anything besides a tourist spot due to that. Bostonians still exist and need green spaces to live and play.