This question pops up regularly.

The answer is obviously a mixed of all the logical reasons most posters eventually write: more attentive and cautious guys, hotheaded cowboys are short-lived (trimmed out, discouraged by the upper echelons and promptly taken out by LE), less overall action compared to the golden age, cultural and demographic attrition, top-tier schemes and crimes that take a lot to infiltrate/investigate/take down, as well as low-tier crimes that aren’t a priority for LE, etc…

Has been like this for quite some time.