Not every month, but the crews are trained a heck of a lot still. I don't wish to start listing them all here but there are dozens of required of things. Not to mention in keeping the training system and administration up-to-date etc.
The costs are divided on monthly basis since we are not calculating the qualifications and trainings of individual pilots or cc's but the things as a whole. And if you have a even a medium-sized airline there are people visiting the training center every month/week over the year.