It was arguably one of the first (the first?) multiplayer RTS's in existence, so there's probably a significant nostalgia factor... but some of the points being

It was arguably one of the first (the first?) multiplayer RTS's in existence, so there's probably a significant nostalgia factor... but some of the points being - in order of significance. * In-game map changes. You could create your own walls, moats, mines, create rubble, etc. in game, so everything was very dynamic, especially once you had several players going. * (mostly) limited resources. Trees were required to build walls and boats, but there wasn't an unlimited number of them. Even after they were all used up, more would grow ( although if you had some around they would grow more often). Bullets/mines were also limited; you had to go back to base to refill, and you could also use up the base's resources if you were too aggressive. * Easy to learn/difficult to master. Bolo had just about the right balance for this. * Headless network play. No server was required (a matchup server existed, but not required); any particular player rage quitting didn't end the game for the rest. * Bug factor. Not quite sure how this phenomenon works, but like the bugs in the oddly popular Goat Simulator there were a few glitches in Bolo that you could take advantage of - without cheating - for a (slight) advantage. Not aware of any games in the last 30 years that have a similar balance.