It is more than just a choice based on cost. Gliding requires you to spend a fair bit of time at the club helping others into the air just as they will you. So you are probably looking at spending a whole day there to get 2 or 3 short flights in, to start with. If you take it up longer term, it is more of a social thing, devoting time and volunteering to help your club function. And that really suits some people.
You can immerse yourself in a powered flying club in a similar way but no-one is going to complain if you just turn up and fly. Slightly different cultures.