lol pal this is such a baseline syllogism from observed behavior and market dynamics, the onus is on you, not me, to empirically demonstrate MacOS market share has decreased. It's that stupid of a claim.
As for the supporting arguments:
Gaming has to do with developers finally realizing Apple doesn't give a f$&& about gaming, the switch from OpenGL to Metal expedited this and further abetted the uselessness of MacOS as a gaming platform (tho it could be reversed due to the ARM transition!)
The TurboTax software is explained with similar ease. The web has won for **** like that, and probably the previous investments in the MacOS userbase for CRUD apps went poorly ^1, probably the web improvement and past experiments led to a different decision down the line from the C-suite guys.
1: What has not gone poorly is Adobe and Creative softwares use, or programming stacks. Did you see how attentive Adobe has been now vs then from PPC to X86? MacOS just didn't have the sway. It sure as hell does now.
MacOS is for three groups: Software devs, creatives, and anyone who both can and wants to be fully invested in the Apple ecosystem. It's not shocking accountants and gamers are uninterested. Apple don't care about them, and I don't blame them.
And the third group has grown due to IOS use, and I suspect this group has played the major role in MacOS' share growth.
EDIT: Aggressive commentary removed