this is not isolated to microsoft, or the US. Everywhere I've worked, the contractors we've had have been treated like second class citizens. The smart ones even insist on it.
Why? Because if they are allowed to enjoy the amenities of a normal staff member (free snacks, invite to company events, etc.) they run the risk of being classed as employees... which is bad news for everybody, not just the company. If you as a contractor are found to be incorrectly classified, that can mean a massive accounting headache, loss of tax benefits, possibly being required to enroll in a union, and lots more.
I've worked in Iceland and the UK, for 5 different companies, each one employing lots of contractors. All of them avoid these benefits for said reason. You can read up on IR35 if you want to know more about the UK rules (although it's been recently revamped making contracting a lot less appealing).
Why? Because if they are allowed to enjoy the amenities of a normal staff member (free snacks, invite to company events, etc.) they run the risk of being classed as employees... which is bad news for everybody, not just the company. If you as a contractor are found to be incorrectly classified, that can mean a massive accounting headache, loss of tax benefits, possibly being required to enroll in a union, and lots more.
I've worked in Iceland and the UK, for 5 different companies, each one employing lots of contractors. All of them avoid these benefits for said reason. You can read up on IR35 if you want to know more about the UK rules (although it's been recently revamped making contracting a lot less appealing).