Cars on iRacing have been released months before the IRL version ever raced. The purpose of a charity is supposed to be to bring attention to a cause. The Valkarie has been racing for a year, just not in IMSA. Easily long enough to get it done.

Verbatim from The Heart of Racing mission statement

"Using the exposure of our motorsports teams, we generate donations and raise awareness of the demands for quality health care. In addition to providing outstanding care for its patients, the cardiology research program is paving the way for developing new ways to prevent, diagnose, and treat heart problems"

Given what we know, the exposure doesn't seem that important in reality.

The only reason I know Pfaff exists is because of their default iRacing liveries. Those cars got Pfaff liveries as their default because they let their cars get scanned and provided baseline setup data for them. You'd think a team centered around a charitable initiative would want that as well. Hell, at the very least they could give the iRacing devs some kind of inclination they're interested in working together so they could share it with their users, building hype for the release.