1) Dealing with climbing the corporate ladder, covering your ass from backstabbers, and all sorts of company politics are bad enough to deal with in fairly small companies where you might have a handful of business relationships to deal with, let alone in mega-corporations where you might be working in one small project department with dozens and dozens of people and several layers of managers.
2) Big companies have essentially become centers for identity politics, not sitting down and writing code and solving creative problems. Somehow good things like being kind to all and treating everybody as you'd want to be treated have morphed into (mostly people who have infiltrated HR departments) preaching anti-whiteness and anti-male hatred. I do some consulting for companies and have been put on a handful of their internal mailing lists so I directly see what kind of racist filth goes out to the actual employees.