Hello! Actually, it's never been a secret.
The way Matchmaking in MA currently works can be described via the following steps:
1. A player enters the Matchmaking queue.
2. The system matches them against players of a similar SP range. The Matchmaking time is 15 seconds for CPC and 30 seconds for all other Modes (Hangar Showdown is not considered, as it uses a completely different system).
3. If a player isn't matched with any players in those 15 seconds, then the system just fills the lobby with bots and sends them into the match.
Alternatively, if a player enters solo, the algorithm matches them against another solo player of similar SP who is also in the Matchmaking queue, or against a team of 2-3 people if there are 1-2 other players in the solo queue. If players are entering as a group, the Matchmaking matches them with another group with a similar number of players with a similar SP range.
Matchmaking is not cross-server (mainly to avoid ping issues), so if you're not getting many players, it's probably because there aren't enough players in your region with a similar SP as you.
Regarding the bots, their strength and equipment are tailored to the game stages (early game, mid game, end game), their AI capabilities, and also to showcase the variety of content to players.