I'm not a lawyer, but it is my understanding that using a GPL library on the frontend triggers the "distrubution to users" clause of GPL. It's a strong copyleft license, turning the entire frontend portion of the application GPL-licensed, which means any user can now request the source code for it. That's an IP risk for any commercial code, and many companies shy away from GPL. Backend use of GPL should be fine since there's no distrubution (AGPL "fixes" this, and such libraries should just be avoided in commercial settings).
I've actually heard this from lawyers before - essentially that if you use a JS library that is GPL and that code gets sent to the user via the browser, that its now considered "distribution".
