Watching the 1990 Royal Rumble match right now on the network, and there’s a little spat between Macho Man and Roddy Piper. How did we not really get a feud between these two? They had a brief encounter in WCW but nothing in WWF. What happened there?

Heel face alignments and retirements never really matched up.  Closest chance would have been 1990 obviously, but they both had other stuff going on.  

Looks like they did indeed do some matches on the house show circuit in 1990, where Piper went over a bunch of times, but I don't think any of them made it to TV or video.  Also it looks like they had a pair of IC title matches in late 1986 in the Pacific Northwest, and I can also attest to them advertising the same match for shows in Vancouver at the time before it was changed to Ricky Steamboat challenging for the belt instead as a surprise.