Apple has clearly focused on iOS and iPadOS the last 10 years and they tried to slowly phase out the Mac but people kept buying Macs so they begrudgingly started focusing on it again around 2016-2018.
The world of iOS and iPadOS is meant for touch and caters to the consumer. Mac OS is meant for mouse and keyboard caters to consumers but it also serve as a development platform for its app ecosystem. As such it need to get out of way too.
Both platforms fulfill different needs. I'm personally glad Mac OS does not look nor behave like either iOS nor iPadOS, even though Apple is definitely trying to add a bit of the same UI with each Mac OS iteration.
Apple wants to have its cake and eat it too. They've been trying to polish the iPad experience enough without encroaching on the Mac market to the point that they're painting themselves into a corner.
iPadOS looks fine for most mobile computing tasks, but it's still seriously lacking as a fully-fledged OS, which more and more people are asking for now that the iPad ships with the M1 chip and a decent amount of memory.
At the same time they required you to own or have access to a MacBook if you wanted to write Apps for those platforms, ensuring there would at least be some demand for the platform. They also transitioned from a proprietary and dated Power CPU to the commodity Intel x64 CPUs reducing their development costs.
MacBooks got adopted at places like MIT as cheap powerful Unix machines and as the LAMP stack took over the internet they became the preferred developer's box. These were the seeds planted.
Now days they're a lifestyle/prestige item for college kids, soccer moms, and corporate executives. They're focusing on it because the platform is approaching critical mass.
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Often times users are confused by how the UI responds or doesn't and the last few years of iOS/Android releases have focused heavily on UI refinement to effectively communicate visually what's happening.