Apollo couldn't have proven that Machi hadn't worn gloves, so it was a moot point.

Now, I don't remember exactly when during the case this was revealed, but Machi's fingerprints were found at the crime scene - on the air vent! Wasn't that one of the major reasons why he was charged in the first place? Since the prosecution's case was built on that, then at least from their point of view, Machi COULDN'T have been wearing gloves at the time, and thus not checking the fingerprints on the gun would be a HUGE oversight, right?

I suppose it would have been possible for him to have wiped the gun, but since in the beginning they thought the murder happened in the third set, Ema and Apollo entered the room almost immediately after the "gun shots" - was there really enough time for him to wipe the gun, and THEN run across the room and up the air vent? And that's not even considering the caliber of the murder weapon, which really should have at least slowed him down significantly...

In short, there were a lot of oversights.