I'm not sure exactly. It was a bank so I guess it was something to do with wanting to appear professional.

There were all kinds of rules and strict dress code, no dyed hair, no personal effects on desks, no mobile phones, no visible tattoos etc.

Not the most fun place to work, so after about a year I actually left for a job with longer hours and a worse salary.

My wild, bystander-who-knows-nothing peanut-gallery guess: some manage-osaur had the internet use logs mined and found out that a lot of people were on Youtube (for music) and decided that people were "spending too much time" "on" Youtube.

Nope, personal use of the internet was banned too. Although that rule didn't seem to apply to anyone over a certain paygrade.