what you’re saying isn’t inherently wrong. If aviation was a declining industry (let’s say like Kodak film dealing with the rise of digital / phone cameras), as work dried up over time airlines would get rid of aircraft as leases came up, lay off staff etc in the same way that Kodak have closed factories, reduced output etc. While tough for all involved, it’s a part of how capitalism works. Companies, industries rise & fall along with the market.
The situation airlines have is more akin to the closure of the car plants in the 80s / 90s - the government deciding they were non viable and pulling the rug from under them (in this instance via quarantine, or state aid). Airlines are still geared for 2019 levels of output, and have no support to gracefully shrink to a more appropriate level for the market.