Is Excel 2024 the same as Office 365? Otherwise that's another extra version they're maintaining.
I have also heard, as you said, that they've "downsized" their QA department.
Regardless, Microsoft seems to have an unfathomable amount of software that they maintain. Like, why is Microsoft Server 2012 still in the extended support window? The fact that even today they're still doing major long-term versions based on year seems completely antiquated.
They keep bending over for these antiquated companies that have a terrible development process that traps them on old versions of software. At some point, the US government needs to step in and force all these companies to modernize and invest in tech.
Companies are basically offloading the cost of maintenance onto Microsoft in a really inefficient way (keep maintaining old versions with patches), instead of just upgrading and staying up-to-date with the latest version.