My gen 1 WK was 100% reliable....after I broke a bunch of stuff, replaced the upper/carrier with a TNA steel upper/carrier, added an adjustable gas block, brass bushing and installed an aftermarket trigger. And replaced all the small parts in the bolt because it developed extraction issues due to low quality chinesium.
Mine cracked a carrier that took out a guide rod, chewed the hell out the upper right out of the box due to their awful machining tolerances of their magnetic charging handle (we were told that was normal lmao), broke a dozen threaded handles with their new carrier, cost me two round trips to the gun shop because the top rail wasn't made to spec so neither the Eotech and Vortex UH1 I bought would physically fit on the rifle. And that trigger, the grittiest 11lbs I've ever touched. Whatever chinesium it was made of didn't improve at all after 15 minutes of doing the paracord trick. It literally went in the garbage.
Great fkn rifle, so quality!
Some guys claim to have great accuracy from theirs, mine must have been made on a Friday. With multiple kinds of match ammo, a geissele ssa-e trigger and my 5-25 Midas Tac I couldn't put 5 rounds under 2.5" at 100m. It's a 4 moa rifle at best with bulk, worse than an x95 by a fair margin. And dear God does it copper foul, you can feel the machining marks in the damn barrel while cleaning. Like cleaning a washboard.
Mine came with a pinned gas block, so I never killed a piston. The new ones aren't pinned so you'd better use high heat loctite and check often or you'll add yourself to the large number that have snapped pistons. The only thing that improved with the gen 2 was the charging handle issue, all the other issues remain. And you get to pay $400-500 more than we did for our gen 1s.
So the answer to why they're unpopular is because they're bottom of the barrel quality that they happily overcharge you for because they know your options for affordable black rifles are limited. You'd be MUCH better off buying a SU16 or finding a T97.