[r_singh]

It's common sense that these SaaS products are targeted towards people who use them enough to pay for it, monthly.

The reason why it's better for the creator to offer it paid only, is that they can focus on shipping features only for those who care about their offering enough to pay for it. These users could be described as power users in comparison with people who expect the service to be free.

The website FAQ even says that this is for professional use, which means that the person who's subscribing, needs to use this on a day to day for their work (or something that's important to them).