We all recognise what is meant by a fruit tree. It seems a better title than Rosaceae, but in fact most of the fruit trees in the park are members of the Rosaceae family and so are many trees that we would not ordinarily think of as fruit trees – but they do produce fruit, just not the kind that we humans eat.
Most of the fruit trees are in fact Cherry trees and are ornamental Cherry trees. If all the individual species of ornamental Cherry were grouped together they would probably be competing for first place as the most common tree in the park.
There are other fruit trees which are not Rosaceae such as the Black mulberry, a member of the Moraceae family. As it is the only Black mulberry and the only Moraceae it stands to reason to simply group it together with other fruit trees.
The apple trees, including crab-apples, get their own page simply because there is a reasonable number of them.