Why does community theme arrangement randomise every time?

I am trying different themes to see which one suits me.

But every time, I open it, the sequence randomises and I can’t keep a track of which theme I tried last.

Same here. Annoying at the least! I thought I was the only one, otherwise I would have put it in Feature Requests.

I believe it is a design decision to help surface new themes.

See here for a feature request to add more control: Sorting, date modified, and view modes for Community Themes plugin