In reply to Sally G.

From a technical standpoint, columns and galleries are not the same thing. I would describe them both as different subsets of layout grids, each with their own pros and cons. Columns don't have rows, for example. You could fake them with the Columns block, but you couldn't do things like equal-height image cropping with it, automatically switching all the image sizes at once, or just any bulk operations on all the images in the group at once.

And, there is certainly nothing wrong with a user building out a custom image layout via the Columns block. However, it's simply easier to get images loaded up and laid out automatically with the Gallery block.

I could also potentially see some accessibility concerns. Or, at least there are semantic markup issues using Columns if you are, in fact, building a gallery -- in my mind, that automatically creates accessibility issues. The end result might look OK, but the under-the-hood stuff would be problematic.

From the user experience end of things, I would think the average user would jump to using the Gallery block before the Columns block to create an image gallery. It might not be until later (after adding their images) that they realize there are some missing features. So, it makes sense to round out the feature set of the Gallery block, which is the common starting point.