4 Reasons you are not able to find bugs

1. Lack of Scanning/Enumeration

The most important part of finding bugs is scanning, the more you know about the target the easier it will be to find vulnerabilities. mostly the bugs that require less scanning are already submitted, you might be lucky if you find bugs easily sometimes but if not then you need to really dig into the target and find some vulnerabilities. Most of the bugs depend on Enumeration.

2. Being Tools/ Script Dependent

Running an Automation Tool or script can save you time but before just being dependent on it you should explore the target by yourself for more knowledge. and yes scripts are easy and cool but being dependent on them from the beginning is not good at all, plus automation tools can miss a lot of bugs so you should recon yourself too.
Additional point: Making yourself a tool can develop your developing skill too.

3. Not Learning

Reading bug reports, writeups, hacking books, and solving bug bounty challenges can be really great for you to learn new things and new ways to find bugs. Keeping your knowledge up to date is the best thing you can do.

4. Not being Patient

Not giving enough time to bug bounty or target, bugs are not easy to find sometimes you can find them in minutes but some may take months so you need to be patient believe in yourself, and keep searching for vulnerabilities.

Keep learning and exploring :)