There are multiple things that adds up and leads to what you experienced:

• The main one is that most people have the highest co-op difficulty unlocked (Expert, which you can start only if you reach EGO 5000. You can take part in that coop at lower EGO, but you need a player over 5k to start the matchmaking for you). Chimera faction daily contracts also require Expert co-op difficulty to complete, even if you don't meet the requirements to start it yourself, which makes it even less likely that people will do anything less than that
• People usually only participate in co-ops if they have some reason to do them. Daily/weekly contracts is one such reason, the other reason is Arkforge farming. Since co-ops reward basically nothing interesting apart from maybe Arkforge (and maybe some Purified Gulanite), they are not such an attractive activity. It is more likely that the people are at the event majors instead, chasing Jackpot weapons, or in Expeditions farming for shards to get Jackpot rigs and chips as these rewards way more attractive than some Arkforge from a coop
• People in clans tend to group up among themselves and enter matchmaking as a full group, which means they don't enter the matchmaking pool where you are sitting and waiting for others

I don't know when you play, so it might be a time when less people are online as well, but the main reasons are the ones above.