The product is fairly simple technologically yes, but the value is provided by making it easy to use so the customer saves time (= money). To do that you need a few UX people plus some developers (especially with web and mobile apps), call that 15 engineers/designers total, plus another 5 for ops. Now you need a sales team since your real money will be in selling to enterprises - call that 15 people. And on top of that you need customer support, and call that another 20 people. Now that we're up to 55 people, we need another 10 people worth of HR and 5 bean counters, that takes us to 70. Now cap it off with 10 managers/executives and we're up to 80, and I'm sure there's some things I was off about or forgot.
It's easy to forget about all the non-engineering resources you need for a medium-sized business.