Building a Time Sensitive Side Project

I am building theupset.co, which is a March Madness survivor pool game. You pick a set amount of winners every day throughout the college basketball tournament without losing. The hard part is you can only pick a team once and if you lose, you're eliminated.

My challenge has been that interest in the college basketball tournament is so seasonal and confined to just a few weeks in March that getting initial sign ups or interest has been a real challenge. I've tried direct outreach to college basketball fans and some social media ads, but the interest just hasn't been there.

Has anyone dealt with similar problems where their projects were focused on a specific time of year? If so, what did you do to generate interest in the "down" parts of the year?

Any and all suggestions appreciated, thanks!