So let's say he takes the 5th but coppers coerce, bully, etc. him into either revoking his taking of the 5th or convince him he's not incriminating himself (when he is) so he talks. What then? And, come trial, let's say he claims he was bullied, who do you reckon the jury's likely to believe? I mean, it's all too easy for that lawyer in the video you posted to say 'Don't say anything!' when he's not the one under the pump and/or blame the person under questioning for getting themselves in the ****. In real life, not everyone knows their rights and nor should they be brutalised for not invoking them if they didn't fully understand the extent or subtleties of them beforehand let alone in an interrogation. Not to mention, it potentially gives the defenders a lot more to work with come trial.
Have to be careful and it's not as simple as 'you didn't invoke your legal rights, sucks to be you' when you're dealing with real people. That's a **** way to protect or prosecute people. Yeah in an ideal world, everyone would know and understand their rights but it's not always the case and people, even this ****, need to be protected from abuse of that. Not least of all because it's more likely to result in the right outcome anyway.