Well I only play Wild because restricting certain cards always felt wrong to me. I always felt that you're supposed to play with everything the game has to offer in order to enjoy the game the best. So If I would ever meet someone with a standard deck in wild (and I'm sure it could have been be me at some point) I would assume that they just want to be placed against every possible outcome the game has to offer.
Imagine this :
They are not that good at deck building and a streamer come up with a great idea for a standard deck that might be super fun to play. Why not play this deck in wild so you can actually face the real dangers ?
Cause Wild is not for old decks or weird combos, it's for everything. It's the real game, with all its flaws and stenghts. Yes your deck could be improved with some wild cards, yes your deck might be made to counter a certain standard meta, but if you just want to play some deck you've seen in the environment you like, what's the matter ?
I don't even notice when people are using standard-only decks in wild, honestly, but I don't like playing standard most of the time. Wild (in theory, at least) has far more diversity in deckbuilding and play. In practice, most opponents don't actually take advantage of the possibilities.
gee' i don't know, maybe they dont have enough cards but they want to experience this "new" gamemode anyways? this gamemode that their friend told them about because for new players unlocking wild is something rather obscure and exciting since you have to craft a wild card to unlock the mode and for that you have to do some shenanigans with the my collection filters, and none of this information is neither obvious nor detailed somehwere in the client.
When I was climb in wild one year ago with Kingsbane Rogue (Mill variant) I saw so many Zoo Warlocks with Keleseth and heal package (Standard deck that didn't run any Wild cards) and now when I was looking at hsreplay I can see that the same list is still playing in wild (link). I don't get it...