Why did some of my fruit trees not grow to the next stage?

If there at 12 or more other trees (stunted, growing, or fully grown) in the 9x9 grid surrounding the tree, the tree will not grow.

For example the stunted tree near your head has 12 other trees trying to grow around it:

To get your trees to grow properly you need to space them out more.

Alternately you can grow them elsewhere and then move them into this pattern. Trees won't grow this packed together, but if placed fully grown into this configuration they will still produce fruit, wood, and other tree resources.

Source: https://gamewith.net/animal-crossing-new-horizons/article/show/18578