It's not that they can't mark it as resolved. It's just that it is bad business to do so.
How they handle the communication on the incident is crucially as important as remediating the original cause.
Just the fact that they are doing this means I will probably never use this service or recommend this service to anyone else.
Okay so let's just say you are one of those affected users
The founder of the company has already emailed you with details and their support team is around for you to ask any follow-up questions. Also the bug/exploit has been fully fixed
At this point are you saying you would actually be upset and leave because the incident on their status page has been marked as resolved?