I think they did at the beginning, there's been a lot of algorithm changes before but once they realized they were losing, they just gave up.
The incentives are just not aligned anyways, Google Search gets its money from the ad links on the top, they don't really lose anything if the links below are half terrible...
Matt Cutts made it seem like they were serious about it. On reflection, his departure seems like a turning point, albeit perhaps coincidental.
Well, there were algorithm changes like Panda 12 years ago...
12 Years is a long time... fighting "the previous war" doctrine type results. Not to dismiss any non-public changes, but never the less, search results quality has suffered. Maybe search results isn't their funnel to relevant ads but rather they want to serve up ads while skipping the quality results step most people expect.