Its liability or selfishness. Ive let kids fish on my property and hopefully it helped them. The last 2 knocked on my door and politely asked. I told them they could, with a few rules. Catch and release only, and they could only fish if I was home. It got to where they started coming by too much, wanting to take my boats/kayaks out, asking for fishing tackle, etc. And I know they had kept some fish secretely. I put up with it, hoping to make a difference in their lives, and they eventually quit coming by.
I think that relates somehow to your post. Dont blame the owner though. People are lawsuit crazy in our society.