Because before the first round he was considered a nobody, and the second round was scheduled to happen two weeks after the first round. It's too short of a time.
2 weeks is more time than the 6 days since the election. They could've decided to stop things then. I get what you mean agree it's probably messy with the timings, but one gets the feeling that if you lose you can do all the election fraud you want, which is kind of suss to me because people can use decoy candidates for the fraud and if they lose nobody looks into it.