States/Cities offer tax breaks to attract/keep the business in the first place. The Pacific NW city wanted to become a tech city and offered incentives (=tax cuts) many years ago for companies like MS to settle here. Successful companies bootstrapped satellite dependent businesses (the myriad small IT shops in area, like SourceDynamics Inc) and attracted in the area subsidiaries from big SV (FB, Google etc). The affluent workforce they foster spends their disposable income in the area and this benefits all other businesses in the area. And both MS and Boeing can decide to move to other locations, taking with them huge swat of tax paying employees and a myriad of satellite smaller businesses that depend on the 'mother ship'.
Here is a simple thought exercise: salaries -> area desirability -> high property taxes -> high budget.
I don't think this is a case of corrupt WA politicians being in the pocket of Big Business Co and writing off tax breaks for kickbacks. I think is a calculated deal in which tough negotiators for both sides reach an agreement benefiting both the state and the business. At 83.4 billion $ budget ([0]) WA state does not seem to get the short end of the stick...
[0] https://en.wikipedia.org/wiki/List_of_U.S._state_budgets