I actually just upgraded my Dell Optiplex 990 SFF to a new full ATX case and had to get a new motherboard. Dell does some funky stuff to their motherboard to get it to fit into their custom cases. For instance the CPU cooler clipped into the case through the motherboard This was one of the ways the motherboard was secured into the case. The other mount points were entirely non-standard so no other case would fit. I did consider making some modifications to the case with a hacksaw before deciding to just get a new case and motherboard. The new Motherboard was pretty cheap because I was using a 4th-gen intel i3. Not great specs but good enough for a homebrew NAS.
My neighborhood has bulk trash pickup monthly. Most of the bulk trash gets put out the week prior to pickup day. The majority of this trash doesn’t make it to the dump! People with trailers come by and pick up anything remotely usable. I like to think they are reusing/upcycling this stuff but I really don’t know. I see this as a huge win because it keeps stuff out of the dump but it does feel very dystopian to see a junk economy like something from Fallout.
I’m in the USA btw. Others have pointed out that some countries have different laws regarding ownership of trash. Don’t get in trouble with law enforcement, get to know your neighbors better! It’s not trash if they give it to you.