There are two separate issues here - one is Buzz, one is KLM's discontination of the STN-AMS route in (IIRC) 2002..

Buzz, like BA's Go, was an attempt to compete with the low-cost sector. Buzz was a good airline, but it didn't succeed.

The reason KLM pulled out of STN is that by 2002 STN had very much found its niche as London's LCC airport. It wasn't just KLM that pulled out, other legacy carriers (like LH and SAS) all pulled out of STN at around the same time.