Although in Derren Brown's case, one of the things that makes him a genius in the world of magic is that he reversed that dynamic. One of the brilliant things about Derren Brown's "brand" of magic is that by blending stage hypnotism and parlour tricks, he does a lot of things where when you think you're watching a demonstration of stage hypnotism, it's actually a parlour trick that is dressed up to look like stage hypnotism.
In other words, he might use a classic sleight of hand trick to do a "force" while finding a way to frame and present it as if he were using suggestion.
But stage hypnotism and suggestion .. .that's not magic tricks. So if Derren Brown is employing a psychological force, or doing a demonstration of suggestion that will work for the majority of the audience but not all ... that's not a magic trick. By definition, it is not a trick.
What magicians mean when they talk about "forces" are ways to make it look like the spectator, ANY spectator, had a free choice but it was engineered. A card force, for example, where you think you have a free choice of any playing card but the magician "forced" a specific card on you. Those are 100% guaranteed. They don't use suggestion, they use sleight of hand, and there is no person in the world that those don't work 100% of the time on unless the magician makes a mistake.
Back to Derren Brown, although him and Teller are close personal friends and they don't hate each other by any means... P&T have been very outspoken about the fact that they consider some of what Derren does to be unethical, because he presents magic tricks as if they are displays of stage hypnotism or suggestion. Like most "mentalists" he has flirted with a line that many magicians will not cross. Where he claims that by reading body language, or using applied suggestion etc. that he can do or know certain things ... when the reality is those things are executed via traditional parlour trick methods are often just classic magic tricks that most magicians know and can do but are presented with a new/different layer of lies.
So why doesn't magic work on TV ... well, you gave the answer by invoking Derren Brown. If he is doing these "forces" (which to clarify I think you mean psychological "forces") and they work 10 out of 10 times on television but they don't work on 100% of live audience members .. well then you know why magic is weak (at best) on TV ... because all we need to do is go ask 52 people to think of a playing card, and guess that they're thinking of the 7 of Hearts (for example), and then just only air the one take where the guess was right.
There is a YouTube creator named James Hoffman who is a coffee barista. And he was on an episode of Derren Brown's Trick or Treat (if I remember those details correctly). His story of being on that show is very illuminating. He talks about how he was shown 2 different tricks, the first one fried his brain, the second one was "meh." For whatever reason they aired the 2nd one that was "meh", but cut in the reaction to the first one where he was like "OMG OMG that was so amazing."
Why would you trust what magicians tell you, when they say they don't do shit like that on television? This is why, as a huge fan of magic, I kind of hate televised / pre-recorded magic. I have no idea what they did during the editing process. Whereas live, there are so many more restrictions and the audience has a much clearer understanding and impression of what those restrictions are. But on tv... anything is possible through editing and vfx.