I'm aware that this is pretty low on the list of problems you'd hate to have but it's there nonetheless. Let's say a relative has heard me talk about some Arduino project I'm messing with or something to do with building a computer. They don't know much about either of those things but they know I like "techie" stuff and gadgets so they get me a gift card from Best Buy, as that is the only electronics store they're really aware of.
Now I've got a $100 gift card to a store that either doesn't sell any of the things I'd want to buy or charges a hefty markup over what I'd normally be willing to pay. Sure, I could sell the gift card to some bargain hunter for $95. They'd get $5 off, I'd get most of the value to spend elsewhere...
...but that's a hassle and not at all what the gift-giver would want to necessitate anyway. The other major option is to just suck it up and either buy something I don't really want/need out of the available Best Buy catalog or maybe buy that $100 item that I would've just found for $70 at Microcenter or Newegg.
I think you nailed it when you pointed out issues of perception and tradition. Giving cash to someone other than an aging/retired parent or a young child comes off as odd. It's almost like you didn't care enough to think of a gift that they would actually enjoy or shows that you know them. I just think gift cards are about the same in that regard, only less desirable or useful.