No one has done anything like a nanoassembler. I know there are
numerous issues to do an actual nanotech nanoassembler, but why hasn't
anyone made macro scale assembler?

I'm thinking of something like a system of tiny swimming lego blocks.
You would drop all the blocks into a fishtank and then direct them to
assemble.

It never crossed my mind!

But then I don't have a fish tank, although Steph53 certainly has - so
she's got no excuse.

Also, I got rid of my Lego set ages ago, although I bet that Steph53
still has hers and, even if she hasn't, I will buy her one.

C'mon Steph ... Go for it!

"why hasn't anyone made macro scale assembler?"

   You make a perfectly good observation. There is much talk of
nano-scale machines for performing nano-scale tasks. Some types of
machines have been prototyped on very small scales, but they haven't
been anything with the versatility of "assemblers". Such capabilities
have yet to be demonstrated even as a model.