Double Returns and Spaces

I don't know exactly where all this is coming from, perhaps some secret literary lab deep in the heart of some active volcano but I'm getting tired of everything slowing moving up to two where there once was one.

Take an address for example:

123 Street
America, City 12345

Now, some people are adding a second space after the City before the Zip code:

123 Street
America, City  12345

What's the diff?

Likewise, now people are putting two spaces after periods.  Why do this?  What's wrong with just one? I dunno. I think one looks just fine. I suspect that people who place two spaces (and double space) are just itching to eat up more page with fewer words.   Yes, that's what I suspect.

I'll forgo complaining about double-spacing text; that's bugged me for years.

(Btw, the spaces may not show up correct as I have typed them in on your end. Blame technology. I do.)