Depends on the channel, the day of week and time of day (and the time zone its main constituency resides in) and how long you waited.

There are a few channels I know that are mostly active over the workweek in US pacific time. Others that wake up with the EU, with some extra activity on weekends.

But yes, some channels really are slow and mostly wake up only on specific actions (eg. joining, asking for a question, people answer, everybody gets back to doing their work) - essentially support channels.

Some are that way by design. #python on Freenode is really aimed at being a support channel. Off-topic conversation is practically not allowed (they have a bot that will pm you if you type lol telling you that #python is a no lol zone.)

On the other hand, I'm currently on 6 channels across 4 networks, all social channels with 10-30 people, and people talk near-constantly. It's just a case of finding places where people are - anyone can create a channel, just like anyone can create a web forum or a mailing list, doesn't mean people are going to pay attention unless the creators and first inhabitants put some effort into building a community.