Dynamic DNS has been the default on every Router I've owned, why doesn't it ever work?

Over the years I've had 6 routers and four different ISP's. Every single time that I remember, the router had dynamic DNS as the default. And after about a month of being installed, I would start having issues with the internet dropping out. And yes I restart the router. I'm not really a tech expert, but setting a static DNS has solved my connectivity issues every time.

I'm curious if anyone has positive experience with dynamic DNS? Is there any advantage to it? Or tricks or secrets to get it to work properly?

Edit/Solved: ISP is having local issues, I just found this widely reported on downdetector.com. The ISP is neglecting to report any issues, their website says all is good. Using static DNS from another source solves the issue. Also, "Dynamic DNS" is a setting name inside my router, but is perhaps a bit at odds with industry standard terminology.