If you want to maximize production, yeah, you cut at certain times of the year to force the trees to put as much energy into the fruit as possible. But if you just leave them outside they will fruit as long as they are sufficiently watered and have enough room to grow (and it's not insanely stressed from a drought or heat wave, etc). There might not be as many fruits, and they might be smaller, but it will produce. But ideally you always want to choose fruit or nut trees that are native to your region (or at least your agricultural zone) so that they require less upkeep in general.

Date trees line the boulevards of many Mediterranean countries, and there is no issue with cleanup or rot.

We had a lot of berry bushes at the side of the road in my hometown. Trees were often apple or Japanese cherry blossom trees. And of course the local chestnut tree made up a lot of them. Wich are also delicious. All of them bore fruit and nuts and we loved picking the stuf.

Public works departments already deal with a lot of bullshit from the builder's special trees that are already installed, managing permaculture forests would actually be easier in many ways. Portland Oregon handles this by making homeowners responsible for the sidewalk easement so they are encouraged to plant trees that don't get too tall and don't get too wide with their roots so the sidewalk doesn't buckle. So you get people planting a lot of fruit trees. There is a Gleaning group there that goes and gathers ripe fruit and does stuff with it like applesauce, or there is also a cider made by Portland Cider Company with juices from gleaned fruit they get off people's trees around town. It's pretty good cider.

I think it's a combination of the effort required and sadly the liability too. I would imagine anyone who is saying "feel free to come eat this food" is exposing themselves to lawsuits, to some degree. The kinds of organizations who are large enough to make a big impact by deciding to grow some food on their properties are the same ones who'd be targeted by frivolous lawsuits, costing money just to defend against, and offering the orgs no tangible benefit in return.

To be clear, I don't agree with structuring things this way and I think it's a trash way for our society to work, but growing food in "public" places seems non-viable without addressing that big vulnerability somehow.

Sturdy trees are good in the city, since they are low upkeep and very good for air quality and shade.

Sturdy trees WOULD be good for the city, yeah. Unfortunately we've decided to, in basically every major city (at least here in NA and I suspect other places), plant non-native trees that have low survival rates and are basically all male. Being male, they tend to also shit pollen basically everywhere. I'd imagine you could deal with the fruit falling to the ground in a number of ways, as well. Could put some canopy underneath the fruiting trees, as to collect the fruit more easily, you could just pay people to come and collect enough of the fruit for use in things like applesauce that the rest of the fruit really presents no issue as far as just sort of rotting and draining into the ground. You could set up a bunch of easy disposal compost boxes every couple feet, so you can just sweep all the fruit up and throw it into that.

I suspect a larger problem would probably be that inside of the city the fruit would be exposed to more than an acceptable amount of brake dust, including that which drains into the planter box, and would maybe not get enough light, but I think those are generally problems we should be solving anyways since they don't disappear just because we decide not to plant fruit trees. Brake dust on the fruit or carcinogens inside the fruit means that those things are also going to be going into your lungs.

trees don't need much of anything, they're perfectly capable of growing on their own. I can't imagine they prune any of the fruit trees in my city (beyond like, removing big damaged branches and stuff that just applies to literally any tree in an urban area) and they produce fruit just fine.

Fruit falling to the ground isn't particularly problematic either, like yeah it rots and stuff but.. okay? who cares? it's gone within like a week and if people are really so unable to handle the reality of food then they can toss it in the compost.