When Namco started trawling out arcade compilations over ten years ago, the idea was hugely compelling. For starters, MAME was still in its infancy, and most of us hadn't come into contact with the real cabinets since the mid 80s. The mere possibility of playing our childhood favourites was an intoxicating one, and Namco did a fine job of drip-feeding them over six volumes, six games at a time. They were pretty expensive for what they were, but the concept of emulation was still a novel one. The idea of being able to play the real Ms Pac Man and Galaga at home was something we'd dreamed about since before the Spectrum, so you could say there was pent up demand.
Wandering around those 'virtual arcades' and checking out the promotional material felt like opening a time capsule. On top of that, you'd get a few less well-known games to check out into the bargain, so the educational value was even greater.
But then, of course, MAME grew to the extent that you'd end up with access to literally hundreds, nay thousands of arcade games. Suddenly the novelty value of these compilations dwindled to nothing and we needed more motivation to buy them.