This is, according to another article I just read online, an unintended consequence of Starbucks "open bathroom" policy. Starbucks allows access to their bathrooms for non-customers.
They are, from my personal observation, reluctant to force the homeless out into the cold even if they are not buying anything. One store manager would offer free coffee to those homeless, but well-behaved, individuals. A show of compassion, but perhaps contributing to the needle problem.