Ok to clarify (correct me if i’m wrong!) it sounds like you have a problem a) with over-saturating your existing audience now that you’ve increased the number of events, and
b) ensuring people show up after they’ve signed up.
For the former i guess you need to expand your reach to attract new members. Word of mouth is always one of the strongest marketing channels, so can you run some kind of incentive/reward to encourage existing attendees to bring a new member along?
Because you’re targeting people with specific job title (recruiters), it may be worth taking a look at something like LinkedIn advertising where you can target people by job title amongst other things. If you can figure out a rough idea for how much each attendee is worth to you, then you can know how much you can spend on advertising to get them there.
How are you currently marketing your events?
On the retention side, this thread here may help you:
I do agree with @Mattkendall that no show rates are a real annoyance with free events. For me the normal drop out rate has always been around 50%, but the other day we had an event that was more like 75%! Very hard to predict sometimes as so many things can influence it e.g. day of the week, time of day etc.