What happened to metadata?

I had some photos that were taken with a ZTE phone that were in Google Photos. I wanted to make sure that I had a permanent copy in Apple photos, so I dragged them out of Google Photos (web interface) onto the Mac desktop, then dragged them into apple photos. However, the meta-data that displayed in Google Photos, including the original date the picture was taken, did not transfer over to apple photos!

I thought meta-data was embedded into the image file itself (and in fact, there is a bit of a controversy, since people can inadvertently reveal information about themselves online that they may not want to). So I was surprised that the metadata was not permanent after all, and did not make the transition.

It makes me wonder how secure the metadata is in the first place if it disappeared simply by moving it from one platform to another, and what might happen if I should someday have to move my photos out of the Apple ecosystem?