Wouldn't a house of bricks take a long time to build? Much longer than houses of straw or twigs? As such, wouldn't the third pig's house be unfinished when the wolf arrived? And thus, wouldn't the third pig also have been devoured?
As the cartoon suggests, the three pigs took an equal amount of time. The first two just took shortcuts by using straw and wood, so they had lots of free time to sing and dance, while the pig who built his house out of stone had no free time at all, because it took him so much work.