Where are you located geographically? Do you know the cultivar name? Tree age?

Located in zone 6B Rhode Island tree age about 10-15 years old dont know the cultivar name.

Have you had a soil test on your lot?

Might be something lacking in your soil that the tree needs. Only a soil test will tell.

Do you have sandy or droughty soil?

If so, are you like many others that think you don't have to water an established tree, even in drought? Certain trees don't do well when planted on dry sites, they're called 'moisture loving' trees, so an occasional watering is beneficial for lush, healthy growth when not enough rain occurs.

These are just a couple of the most common of possibilities affecting your tree.

This is why knowing the cultivar name is helpful. Different cultivars will have different growth habits and some will have a thicker, denser crown than others.

I am going to guess that this is either Bloodgood or Emperor 1, as both bear a similar appearance to your tree and easily get to that size in a suitable climate. It could benefit from some crown reduction and thinning and that could simulate some interior growth. You can thin now but wait until late fall for any crown reduction. And if at all possible, hire an arborist skilled with Japanese maples. This is not a tree to practice pruning skills on and needs a very light hand!

btw, there are very few JM cultivars with red leaves that are dwarfs other than the dissectums.