My personal theory is that time machines are like phones. You need to have one person on the calling end and one on the receiving end. In the Deathmatchverse, many historical figures and celebrities are in fact time travellers, and therefore can be brought to the ring. However, Stacy, 'NSYNC, and the Backstreet Boys didn't have time machines, so they couldn't use the Time Machine to get them back.
Why didn't they use the Time Machine to tape all over again the Beatles match (or at least prevent Nick Diamond from getting his hands on it)?
The Time Machine is probably only on set when they plan to do a Time Machine match, which they weren't in the Beatles fight and Backstreet Boys vs. N'SYNC battles.
I don't get the joke where Tally is interviewing Gwen Stefani in the restroom, all of Stefani's answers are fruits or vegetables and the spellings of them, and once she spells kumquat some woman comes out of a nearby stall looking scared or embarrassed and runs out of the restroom. What did she think Stefani said when she was spelling kumquat? Or was she just freaked out by how weird Stefani is?
Might have been a joke about her song "Hollaback Girl". Haven't listened to it in a long while but she mentions bananas and spells the word out I think several times.