Publicly-traded companies, by their nature, cannot be major philanthropists. They are expected to return value to their shareholders, not give it away. If you see a company's name on a charitable event sponsors list, chances are it came from the PR budget, as shareholders are far more forgiving of marketing expenditures than they are of giving to a cause they do not personally support.
Philanthropy, for good or bad, belongs to the people who were enriched by the company. Tax laws around the world tend to support that bias (taxing the rich at higher rates than corporations). If someone's name is going to be on that bridge (or a hospital or university building), it'll more likely be an expression of personal vanity than corporate.
Philanthropy doesn't have to be altruistic. What difference does it make if it is or isn't? I'm sure the hungry child, the abused wife, the scholarship winning underprivileged student doesn't care. A patient is the "xyz corporation" wing of a top rated private hospital isn't likely to request transfer to the decrepit city-run hospital downtown because it doesn't have any commercial sponsorships.
Also many Fortune 500 companies do have separate 503(c)(3) charitable foundations that can free operate outside the demands of its parent's corporate structure.