Speaking as a local, there's a lot of factors at play making Seattle very online:
Firstly: Seattle is a big tech city, Amazon was founded here, but like, there's offices for all the major tech companies (even ones that are more usually associated with San Fransisco, like Meta, Cisco systems, IBM, ect) Microsoft and Nintendo of America are both headquartered in Redmond, but Redmond is a suburb of Seattle. Same with Valve, which is in Bellevue, Sierra was in Renton, (heck, Wizards of the Coast is still in Renton) there's video game studios all over, so naming them is cheating when it comes to tech companies.
Back in the day it was all Boeing, but before Boeing there were others, basically my point is there's multiple generations of engineers here, both locals and transplants.
Second point: There's a lot of queers here. and I do mean Queers as in people with non-normative gender/sexuality/presentation going on. SF has a reputation for being The gay city, but it's too expensive these days for a non-tech person to coast on the goodwill of their extended polycule for long. That person tends to end up in Seattle. (or Portland, but there's not as many jobs in Portland)
Washington State is specifically a magnet for trans people because if you qualify for Washington Apple Health, you qualify for free gender-affirming care. (not all clinics take medicare, but there's a large number that do and it's Very easy to get HRT, your local planned parenthood hands it out if you tell them you want it) So, we especially get all the trans people from all over the US. Basically, if you're too poor to move to Canada, but you're gonna die if you stay in Texas/Florida/Alabama/ect ? You are moving to Seattle.
Which leads us to our third point: Polyamory is normal in Seattle. There's a lot of weird relationships going on around here, perfectly normal cis couples will have a third they have fully integrated into their social life. This is a normal activity for boomer-aged folks even, it's not a recent phenomena, it's part of the existing culture.
(The big polycules actually present a weird problem you don't get elsewhere, because they take over nonprofits, and you don't realize that dating the polycule is a requirement for volunteering until they kick you out for not being a "good culture fit" I assume this is also a problem in places with cults, but it sneaks up on you here in secular spaces that are allegedly "queer friendly" watch out if there's only one kind of queer!)
Fourth point: Unfriendliness. as mentioned the city is full of techies, but all of them complain about the "Seattle Freeze" which is when nobody wants to be friends with a guy who is going to leave after the next round of layoffs.
Locals are generally standoffish about making new friends, especially if they perceive you to be a flight risk. we all have a lot of internet friends who used to be local, and every day our internet friends move here.
Because all our friends are online (you can't afford to stay if you're not in tech, you didn't marry a techie, or you're not dating at least two) all the locals are online. Because they're a bunch of homesick techies? All the transplants are also online.
Because they built the internet, all our folks are online.
Five: Everyone in Seattle is Online. Everyone has always been online. if you find a website with a really short catchy URL that was obviously nabbed in 1995 (the woodland park zoo is literally zoo.org Ciscoe Morris owns ciscoe.com ) that URL belongs to someone in Seattle.
"average queer has three nonbinary therian girlfriends" factoid actualy just statistical error. average queer has zero girlfriends. Spiders Georga, who lives in Seattle & has 10,000 puppygirls in hir polycule, is an outlier adn should not have been counted