http://www.ign.com/articles/2014/07/04/how-pac-man-joined-the-super-smash-bros-roster

Though the latest installment of Super Smash Bros. on Wii U and 3DS will be the first to feature Pac-Man, his inclusion was actually mooted by Miyamoto far earlier.

Writing for Famitsu (via Kotaku) Smash series creator Masahiro Sakurai explained Miyamoto wanted Pac-Man to feature in Super Smash Bros. Brawl, but he decided to veto it.

“At the time, imagining the image of Pac-Man and his incomplete pizza shape, I thought to myself, ‘Hmmm… That’s a little too farfetched,’” Sakurai revealed. Obviously he's changed his mind since then. “You never know what’s going to happen in this world. I’ll just keep my mouth shut. That’s a good idea,” he concluded.

Seeing as Pac-Man is owned by Bandai Namco, which just so happens to be assisting in the game's development, it's likely that played a part too.