While gold and platinum are similar in price per gram, platinum is more dense and so more of it is required to make a ring. Additionally, platinum rings are usually 95% pure platinum, while 14k gold is only 58.5% gold (18k gold is 75% gold). Therefore, platinum rings are more expensive.
Despite being stronger and more durable, platinum is a softer metal than 14k gold. This means it will get scratched a little easier than 14k gold would. However, when gold is scratched the gold is lost and it looks like a scratch. When platinum is scratched, the platinum gets moved from one place on the ring to another.