It won't be for long! Taxes and spending in Seattle have shot way, way up, far in excess of the recent population growth.
There's an argument that places with lower taxes and lower government investment attract and are better for businesses. The evidence in the U.S. seems to be overwhelmingly otherwise.
The states with the lowest taxes and investment are the poorest; all the great American industries, from automobiles to finance to IT to education to many others, started in high tax/investment locals, boomed there, and remain there. Perhaps investment is a good way to yield returns.
OK, what great U.S. industries were born, boomed, and remain in Texas? Oil doesn't count; that's a coincidence of geology and geography.
I also said states with low tax and investment were relatively poor; Texas' median income is below the U.S. median (which is true of almost all the die-hard red states):
https://en.wikipedia.org/wiki/List_of_U.S._states_by_income
EDIT: A few edits
Kansas:
2000: 2,694,000
2010: 2,859,000
2017: 2,913,000
These are all consistently increasing year after year:
Nebraska, Oklahoma, Arkansas, Indiana, Missouri, Iowa, Minnesota, Ohio.
Illinois is hit or miss, however it's up a million people over 20 years.
Michigan is the only one that has particularly struggled. Its population remains above where it was 20 years ago; it's about 50k people (~0.5%) below its 2004 record high.
Connecticut is definitely struggling, they've seen zero growth over seven or eight years, and comparatively little growth over 40 years despite being an affluent state.
If you look at other rust belt states you will see a similar trend, and I believe it is due to people moving away looking for work, starting in the 70s. The decline of the auto and manufacturing industries here is likely to blame. The same trends generally apply for Illinois, Michigan, Kentucky and Indiana. In Pennsylvania the trend started much earlier which maybe follows the steel industry decline. Anecdotally much more than half of the people I keep in contact with from high school and college in Ohio have moved away, myself included.
The parent was clear about the claim: Kansas and similar heartland states are losing population. It's false.
Over decades there's a massive difference between gaining 0.3% (or similar) population per year and losing 0.3% per year. Kansas gained 1/3 more people over 50 years. Had that gone the other direction persistently, they'd barely exist as a state today. Contrast that with Germany over that time, which has seen maybe 5% growth. Germany would have loved to have 33% growth over 50 years. Or the Baltic states, which are more comparable in size to a Kansas - zero net growth over 50 years. Now that's stagnation.
Or put it into more concrete economic terms. With the additional 1/3 more people, Kansas has an extra $38 billion in annual GDP output today, a total of ~$160 billion. Had they gently gone the other way, and declined slowly over time, it would be more like $60 or $70 billion today. It's a huge difference. They have a GDP per capita higher than Sweden, so when you can organically add 1/3 more people to that, it's a very meaningful economic result.
"The rural population of Kansas continues to decline in a process known as rural flight. The past few decades have been marked by a migration from the countryside into the cities. Kansas now has more than 6,000 ghost towns and dwindling communities, while communities in Johnson County (home to metropolitan Kansas City) are some of the fastest-growing in the United States."[0]
[0] http://worldpopulationreview.com/states/kansas-population/