Because Activision pushed for market, for a product, for release dates, yes. Get shit out the door faster to appease the shareholders and big money men, than what Blizzard was comfortable with, but ultimately had to comply with, given they are owned by Activision and its shareholders. Isn't it obvious at this point?
What's been Blizzard's trademark since before they got bought by Activision? It's done when it's done... and SOONTM. None of that shit post-activision. Buggy shit release one after another, and total misfire of dev time, ressources and management of projects
Games under Activision (2008+) are Starcraft II, Diablo III, Heartstone, Heroes of the Storm and Overwatch.
Of those Overwatch is Titan on a smaller scale, Diablo III started in Blizzard North that was closed in 2005 so before Activision as for Starcraft II 2010 and so 2 years under Activision with a 3 year development cycle even if they carved it into 3 games I have a hard time to blame Activision for it and more Blizzard as they havent put a game out since 2004 World of Warcraft.
And they never had "It's done when it's done".
You are simply flat out wrong. Blizzard ALWAYS had the "It's done when it's done" monicker and the "SoonTM" trademark, obviously because people were hinting at how long development cycles Blizzard games have, but whenever they finally DO come out, they are amazing and full of quality work. Taking your time to perfect a game, without rushing it.
Until Activision and bobby moneydick came along of course, and altered that culture entirely from the ground up
You probably don't remember, but Blizzard actually entirely reworked Starcraft 1, becuase people thought it was "just" orcs-in-space. It looked and felt too much like warcraft 2 reskin. It wasn't up to par on quality, so they scrapped the entire fucking thing and made starcraft 1 from the ground up, crunched through that, and made one of the best rts games of all time, if not THE best. You would NEVER have had that situation if Activision was breathing down their necks.
Diablo 3 pre-production and real production started around 2008 or later, due to cuts and Blizzard North being shut down. so effectively, the game wasn't being made prior to Activision, so definitely after in large aspects
Starcraft II started production probably some time before Activision, but was heavily in production during 2008 and onwards exactly at the time and years after the activision merger. Starcraft 2 was also a good game overall, it has shit story, but the gameplay adn especially multiplayer was solid and amazing, so obviously Blizzard had made good stuff before Activision came along.
Hearthstone is a great game
Heroes of the storm WAS great, but it got shut down and downsized because of Activision. Dustin Browder (who Dreamhaven just hired) was lead director on that game along with Starcraft 2, and he was working on a starcraft fps that activision cancelled suddenly in 2018/2019.