They had already had their allotted playtime on it, and needed to find something else to do.
However I would like to point out that at the begining of every game they clearly stated Go mom! Kick dad's butt". just a little brag(im the favorite)
Peter was laying down playing with his transformers. Finn dumped out his box of Lincoln Logs and was building a
dilapidated shack barn? stable? general store??? ...something with a donkey and a roof and a leaning tower of logs.
He looks over to Peter and they have the following conversation:(imagine Finn doing his script in a sing songey kind of way)
FINN: Hey Peter, wanna play Lincoln Logs with me?
PETER: No, now leave me alone.
FINN: It will be fun!
PETER: I said no! Now leave me alone...AGAIN
FINN: You'll Like it!
PETER: Finny, I dont want to play Lincoln Logs I want to play with my Transformers so go away
FINN: are you sure?
FINN: They're made out of real Lincoln!
PETER: Oh, Okay.
The fact that the logs were made from "real Lincoln" was the point that made peter change his mind.
Way to sell it Finn.
a few minutes later the transformers were visiting this Real Lincoln structure and asked if they could Pet Finns Donkey. Finn said "Sure, he doesnt bite... except on Thursdays"
That kid. Where he comes up with half this stuff, I will never know.