Why do we have a lot of applications in "In-Progress" but just a few in "New"

In-Progress means that you have a candidates who've started the process by filling in their details on the application form, but have not submitted all the answers - yet.

You can setup the reminder email template (present under each job's settings page > email) to send them a reminder to finish their application.

It might also help to either reduce the number of questions - if you see most candidate drop off after a certain number of questions, or you can make a better pitch to the candidates right upfront where you tell them about the job and the opportunity better.

Sometimes all of this also does not help if you're getting a lot of unqualified candidates from unrelated job boards (eg. you're looking for a senior candidate, but the job board that you've posted the job on gets a lot of traffic from candidates early in their career). In that case finding better places to advertise the position might help.