In one of the very old episodes still part of the original (aka, before Advanced Generation) series, he got coerced into trading his Utsubotto for that Koikingu scammer's Utsudon, then Utsudon evolved into Utsubotto mid-battle, and when Team Rocket got defeated, the new Utsubotto was left behind and found the old Utsubotto, and the 2 fell in love with one other.

That's why it's not there.