Unforunately, they are. A large proportion of the tech industry is startups / small businesses. I'd be surprised if Google/Facebook/Amazon/Apple/Microsoft make up even 10% of tech workers.
My current employer employees more tech workers than all YC startups combined, for example.
Facebook - 25,105 employees (https://en.wikipedia.org/wiki/Facebook)
Amazon has 566,000 employees (https://en.wikipedia.org/wiki/Amazon_(company)), but it's unclear how many of those are actually tech workers. Amazon has a lot of retail and warehouse workers, many of who with wages so low they qualify for food stamps.
Apple - 123,000 employees (https://en.wikipedia.org/wiki/Apple_Inc.) Apple's 2014 SEC filing said that half of their employees are retail workers, so let's give Apple 62,000 tech workers.
Microsoft - 124,000 employees (https://en.wikipedia.org/wiki/Microsoft)
There are around 7 million tech workers in the USA (https://www.comptia.org/about-us/newsroom/press-releases/201...)
Even if we pretended that all 566,000 Amazon employees were actually tech workers (they're not) and the above numbers were US-only employees (they're not), that would total to about 860,000 tech workers.
860,000 / 7 million = 12.3%
That means that at least 87.7% of American tech workers do not work at Google, Facebook, Amazon, Apple, or Microsoft, despite these companies being five of the richest tech companies in the world.
Oracle
Cisco
IBM
Dell
HP Enterprise
HP Inc.
Lockheed Martin
Northrop Grumman
Raytheon
General Dynamics
General Electric
Intel
AMD
Qualcomm
Texas Instruments
United Technologies
Analog Devices
Samsung
Phillips
Toshiba
... I'm gonna stop listing all the big tech companies I can think of. I madey point.