Each of these entities requires the work of creating and maintaining a specialized construct (often for profit) - which will then only attract a purposefully narrow audience.
Contrast this with public spaces that are attended by diverse people, because their attendance isn't constrained by ability to pay or having a particular interest.
The advantage of a public space is that it isn't an exclusionary club.
I guess it depends on what you want. Do you want to meet people once, and never meet them again? Squares and parks are fine. But many people want community that is more than a series of one-off encounters. For them, they likely need something more than parks and squares.
Contrast this with public spaces that are attended by diverse people, because their attendance isn't constrained by ability to pay or having a particular interest.
The advantage of a public space is that it isn't an exclusionary club.