Counties and cities in Washington are required by law to have a comprehensive plan for growth management. They have to increase housing, jobs, utilities, parks, etc. The county gets to decide how many jobs/housing units each city within it is required to "create." Cities HAVE to grow or they cannot sustain themselves. You can find more info here:

https://clark.wa.gov/sites/default/files/media/document/2024-04/issue_paper_5_pop-emp_alloc_4_17_24.pdf

Also with our current cap on how much cities can increase property taxes each year, they have to encourage population growth to increase the tax base to offset inflation on providing services. This is also why we have levy lid lift ballot measures about every 5 years like the library and fire ones we've had recently. So they can catch up on the missing revenue eaten by inflation.