anyone knows why the last release is 4 years ago? the tool is so popular that this kind of release cadence seems weird

It works, and does what it is supposed to. Why does it need a new version?

To compete with the newer, blazingly fast tools

What are the competitors in the jq space?

At least jaq[1] gojq[2], and jp[3] (this last of which is jmespath rather than the jq query language)