Because most of those politicians think Google employs roughly the same number of people that GM used to. Google has about 55k employees [0] and GM at it's peak had about 350k employees [1], a 6 fold difference. GM also had high competition in the marketplace with Ford and others, so the number of autoworkers was likely in the millions for the country. Since the car and the computer are synonymous for 'mental space' for most people, meaning they are about equally used in terms of time and resources, the 2 industries are considered roughly equal. Granted, there are a lot more tech companies out there than auto companies even in the 80's heyday, so the number of workers may be near parity.
Also, remember that Google and FB have put a lot of cash in to D.C. in terms of lobbying [2]. FB is essentially using the start-up scene as their R&D departments, occasionally having to fork out the moolah to buy WhatsAps and other viable competitors.
[0] https://www.quora.com/How-many-employees-does-Google-have
[1]https://en.wikipedia.org/wiki/General_Motors#History
[2]https://www.washingtonpost.com/politics/how-google-is-transf...