Government is at fault for companies using legal loopholes to avoid paying their (and I'm not even going to say "fair share of") tax.
That is it and that is all it is. We could argue till the cows come home about "ethical" or "whats right" but we live in a money centric society and it will never change until there is political will to change it. As to whether we should award them contracts does anyone really think the 100m going to another cloud provider would have wielded anymore tax? I doubt it very much.