These are called "chase" cards from the old baseball card collecting days. Each player was printed in 10s of thousands, but certain cards were limited to hundreds or thousands, so that not everyone could get one in a random pack. The true collector who had to have one of every card printed to build a master set would have to purchase hundreds of boxes or buy missing cards from sellers.

Looks like Upper Deck is continuing the tradition by expanding the card set by adding non sports related items so that master set builders have to include these. Its good for us, that they are giving chip collecting another avenue of exposure. UD also has US coins in the 2020 set. These coins all appear to be in average circulated condition and by no means rare, like the casino chips they have in the 2021 set.