each release is one game: this is space invaders, all alone. presumably, they wanted to do an iconic game for the 500th in the series, even if it’s one very few people will want to buy. people have been theorising that that’s why outfoxies came out this week: a big exciting game to make up for the not so exciting announcement.
the more expensive arcade archives games either involved more licenses (because of anime characters etc.), or more difficult (presumably bespoke to the game) emulation. people get excited about them because in many cases (like outfoxies), they’re the first time decades-old games have received home ports of any kind. though emulated, the emulation is better than mame, and in the case of games that use analogue or other controls more complicated than a digital joystick and buttons, they’re already calibrated to be as close to playing the original as possible.
it’s to the extent that the arcade archives release of aqua jet has optional motion controls accurate enough that it’s possible to build your own fake jetski cabinet thing at home, if you’re insane.
there’s also a subseries called “arcade archives 2”, which add online play, and i think are maybe only on switch 2 and ps5?