How can this be common?!?

Went to RSPB Newport Wetlands today. It wasn't the best day of birding I've ever had though we did see a Wood Warbler and a Curlew. The real stars however were the butterflies. How can such a fabulous butterfly be called 'common'? There were several of these beauties fluttering around as well as Clouded Yellows. They looked together.