I imagine it's also bad for their careers. A lot of serious cases are either historic, with no forensic evidence, or "he said-she said" without any independent witnesses or reliable evidence.
When defendant's are found not guilty, which the majority are, it can't reflect well on the Barristers work.
And no, I am not advocating for easier prosecutions, if the evidence isn't there, it isn't there. There can't be a "right" number of convictions for any offence. Otherwise we have Totalitarianism.