Can anyone suggest why they are attracted, and how to
discourage them?

Solitary bees. Just let them get on with it. You won't notice them, but
they'll do a bit of the good stuff that bees do

I've become quite fascinated by bees. I seem to see a different variety in
our garden every day. I'm semi-sorta-tempted to set up a hive or 12 ...

Al.