Because, as I tried to explain with the story of Roy Sievers, AL homer champ, 1957, 1B is an infield position. A 1B must take grounders, line drives, and anything hit to the right side. A 1B does not merely stand around and play catch. Sievers was a good OF, but needed infield practice.
Adams needs to learn 1B before he can play it. When Pineda come back, Adams can play 1B in AAA as the organization trains him.
Adams has played first before. He'll be fine.
