The Olympic Peninsula is a beautiful place for sure, and if you're into fishing you'll likely be quite happy there.
Boating in general is different here - on the coast the conditions can quickly become extremely ugly for your average recreational boat - many a trip is cancelled after a last minute weather forecast check. The Strait of Juan De Fuca can also be quite unfriendly, and additionally there are stronger currents to deal with. It takes a pretty decent boat, a tolerance for cold wind and rain, and some nautical confidence to get much fishing done during a significant chunk of fall, most of winter and early spring. So, the weather and the tides eliminate a lot of diving/spearing possibilities.
Fishing and spearing are fairly tightly regulated in Washington (when I was in California last year I checked the regulations and found them to be quite relaxed - but then, I saw a lot of areas completely barren of fish life when I dove, too). On the coast the regulations are somewhat more relaxed - once you turn the corner into the strait the regulations start to tighten. Have a look at the regulations at wdfw.wa.gov if you're interested. Halibut season is quite short, as is Lingcod, and Rockfish is fairly short too (in fact, most places you cannot spear them at all) through most of Washington. So, regulation (short seasons specifically) is the second factor reducing your chances of spearing halibut in Washington.
The halibut you're dealing with in SoCal are in fact a completely different species (left eyed California Halibut as opposed to the right eyed Pacific Halibut). They're more likely to be found in sport diving depths. Pacific Halibut quickly move deeper as they grow. On top of this, only about 2% of the Pacific Halibut biomass is in Oregon and Washington - the majority of Washington's part being out on the coast. 15% of the biomass lies off BC, and the rest is found off Alaska. There just aren't that many Pacific Halibut in Washington - and very few make the turn in through the strait - most of them will migrate right along the coast and out along the west side of Vancouver Island. If you found one while diving it'd be considered quite unusual. So, rarity is the third factor working against you.
Plenty of spearing happens in Washington, but it is done by divers who prefer to dive rather than socialize. Most popular is Lingcod during the very short spearing season. This board is not a good representation of diving activity in Washington at all. Especially among divers who are largely ignorant of fish stocks, regulations etc, it is currently not "cool" to accept spearfishers. I probably know more about the resource than most of them, yet when I mention that I spear and eat fish both for healthy exercise and for protein they will almost drop the McD's burger they're eating. Never mind the hypocrisy of paying some unknown party to (humanely?) grow and slaughter their protein for them, or the fact that the cow they're eating emitted copious volumes of methane into the atmosphere as it grazed in a field that used to be a forest. This situation is a source of some amusement to me
If you move up this way, hook up with some locals who know the area, and have a great time. Stick by the regulations and always keep in mind that in order to maintain the resource we're harvesting we need to take an interest in the critters themselves - learn their lifecycle and try to be selective so that subsequent generations of tasty seafood can find their way onto your plate.