Hallelujah for this entire organization! Organized lo-buck motorsports are almost always better for the community AND spectators. Unless it's a typo, I don't know why rules would mandate tires older than 2019 but so what - it's easy to comply with.
I confirmed with the HSRA that the pre-2019 tire rule was for cost reasons. Per Jonathan Eckelberg, the director: "A big part of that rule is cost. We don’t want racers in HSRA showing up with brand new tires. It’s an effort to keep it fair for everyone and a more even playing field."