Because they think a library is not a place of silent study, but a place of either
- group study
- checking your Facebook feed
- eating lunch (!)
- or being on the phone to their mates (!!)
Incidentally, having just been subjected to the first three in my local public library, where I came for some peace and quiet,
FUCK THOSE PEOPLE!!!
I don’t care if you’re reciting the periodic table in cute off-the-boat Greek accents. Fuck off and do that at the local café.
The more interesting question is, was it ever thus, and is it everywhere thus? The answer is no. When books were being used in libraries, rather than decorative (so, 20 years ago), there really was a lot less of that.