Over time they just learn how to wear you down.
When they were younger we could set limits and keep it enforced, but as they get older they just kept find ways to get around them. We tried Google's Family Link (poor quality and mostly useless with ChromeOS), per-device time limits on the wifi router, whatever, but there's always some new battle and COVID just threw a wrench in everything.
In the earlier days it was easier to make the argument because we had very tight bandwidth caps on our (rural) Internet. So there was simply no streaming video for them. But that's gone, and now my son (11) sneaks into the living room, puts on YouTube with the volume turned down and the closed captions on and just watches Minecraft and Terraria videos as long as he can. If that gets shut off, he paces around in his room talking to himself about the same video games.
And now my 14 year old is in high school and a phone is just a part of life for teens now that is really hard to separate them from.
And there's always some friend with parents who've set no limits that they can point to and tell you what a fascist you are, too.
(IMHO the really dangerous period is especially in teenage girls from ages 10-13, because there's all sorts of content out there to access that can have damaging mental health effects. For us it was Tumblr and all sorts of self-harm content and I ended up having to DNS block all of Tumblr and a few other sites for a while. With maturity and discussion they learn to differentiate and critique and talk to you about things, but it's really hard to keep them away from The Bad Stuff. I imagine with teen boys it's more about porn, and that's a battle I'm sure I'll have to face soon, too)