Ask HN: Why would Apple cannibalize its macOS/Mac ecosystem?

The improvements bought to the iPad OS announced during the WWDC bring the iPad OS even closer to the Mac OS capabilities set. As a long time Mac OS user I have a hard time why shouldn’t I switch to an iPad with my next device upgrade instead of a Mac. Not sure what Apple is aiming for here given that an iPad is definitely. cheaper than a Mac (eg. an 18GB air).

Any ideas on why would the push the tablets to provide similar capabilities as the macbooks?