As you can see from the data[0] the city itself raises tax through a variety of channels. The largest being property, business, and retail taxes. As you can imagine, when the city grows all those enumerated taxes grow accordingly. As you can see in data[1] the tax receipts for the years 2000 is roughly $600ish million. For the 17-18 fiscal years, according to data[0] Seattle had receipts of $1.1-1.2 billion.
So tax revenues for the city are close to 100% increase. If you see the Census for the year 2000, the population of Seattle is at 564k. For the year 2016, the population is at 750k or so. So a 100% tax revenue increase and a 50% population increase. I'd dare say the city council is just belligerent with other people's money.
Also, there is a legitimate far left socialist on the board. You should watch the Shapiro debate against the Seattle $15 min wage. She's full of ideas with no substance to back it up.
[0]https://sccinsight.com/2016/10/03/understanding-the-seattle-...
[1]https://www.seattle.gov/financedepartment/0102Adopted/City%2...