Last year's series of The X Factor saw acts encouraged to write and perform their own songs.
Eventual winners Rak-Su went on to release an original track - Dimelo - as their winner's single.
But Olly thinks original songs are a bad idea.
"Last year’s show for me wasn’t the show I fell in love with years ago when I was on it," Olly said. “It was very different, they changed it completely, loads of artists singing their own songs.
“For me, Saturday night TV is about entertainment and people want to tune in and be entertained — that’s one thing that I love with working on The Voice.”
He told The Sun newspaper: “When you’ve already sung your own songs on the show, where do you go afterwards?
“You already know what they’re going to do.”
A spokesperson for The X Factor responded to Olly's comments in a statement in the paper: "The X Factor is very proud of its continuing and unparalleled success all over the world in discovering so many talented artists who go on to become global superstars.”
Meanwhile, Olly has dismissed rumours of a feud between himself and X Factor boss Simon Cowell.
He said: “I saw him last year at an ITV event and he was fine. Listen, there’s no beef between myself and Simon.
“We’ve got a great relationship and I’m sure when I see him next we’ll have a drink and we’ll be fine.”
The Voice UK 2018 final airs this Saturday night at 8:30PM on ITV.