Websites change stuff all the time and if you’re having a lot of outgoing links to different sites it might be hard to have control over all of them.
There’s several free services that can search through your website and find those broken links.
One that I like is https://www.brokenlinkcheck.com, it does exactly what it should do and there’s no requirement for a membership. Only a captcha that you need to enter to crawl your website for broken links.