Reusing stones from ancient ruins used to be a widespread practice. I remember hearing a story, not sure how true it is, that the ottomans had plans to use the giza pyramids as a quarry. The practice of grinding up old mummies is almost as ancient as the mummies themselves. Used mainly for fertilizer I believe, and I think it was in vogue as a paint pigment for a while.

I know there are places, especially around the Mediterranean, where you can see foundation stones still etched with ancient hieroglyphic/whatever scrip just thrown in willie nillie.

I won’t condone everything the British museum has done, but a lot of these artifacts wouldn’t exist if they weren’t shipped off. Caring about the past and the artefacts left behind, while by no means new thing, most people for most of history didn’t seem to give two shits. Probably more concerned with not starving etc…