The "risk" lies in not knowing, which may have negative ramifications later.
As it would be impossible to tell the players every single thing their character(s) know about the setting, never mind impossible for them to remember it all if we did, the best way to abstract this is with a "do you happen to know this snippet of info" roll. It's either that or they know nothing, take yer pick.
It's like in real life if you ask 100 people who won the 1949 FA cup you might, if you're really lucky, get one right answer from someone's memory (as opposed to their going online and looking it up somewhere). But if you ask long enough, someone's gonna get it.
Everyone having a 5% chance to know everything is too generous, I agree. That's why I sometimes put it as "If you roll a 20 I'll think about it". That said, though it might not be anywhere near as high as 5% the odds of someone knowing any given thing are rarely if ever outright zero, and I want to account for that somehow.
Every player rolling even if it might be pointless is great design as IME players love any excuse to roll dice!
And maybe - just maybe - the Barbarian overheard someone in the pub last night talking about whatever it is the Wizard and Bard don't know right now.
Never say never.