Why aren't stores forced to use chip & pin everywhere?
"Why aren't stores forced to use chip & pin everywhere?"
I think you have the question backwards: what would force stores to use chip and pin?
Look who gets hurt in a credit fraud:
Usually, not the account holder - if they can prove the fraud is not their fault they usually are not held responsible for most, if not all, of the cost.
Not the credit card company - almost always, they just reverse the fraudulent charges back to the merchants.
So it's only the merchants who have any motivation to deploy anything more secure. However, the "invisible hand" only works when there are real alternatives, and since the credit card companies don't really offer a meaningful alternative to mag-stripe, the merchants have no choice - they take what they can get (mag-stripe) or they don't handle credit transactions (read: they don't get any business, because who can be bothered to carry cash or checks in this spend-spend-spend era?)
I knew of a guy involved with a very large company's web site, who detected a massive credit fraud-in-progress. He held the transactions, contacted the credit card company, said "I can give you the address they are wanting the goods shipped to: call the police, nab them in the act, done!" The credit card company's response? "Don't care, not our problem, don't let the transactions go through or we'll just charge it back to you, bye now<click>".