Technical arguments about end of technical support and ESU aside, it's really just a business decision by Intuit as they determined there would not be enough demand to make it worth their while to release and support a Win 10 version. See post from VP below (fwiw).
Desktop Turbotax revenue ($200mil) is only 1% of Intuit's $20bil revenue, they sell 35mil "units" of higher revenue online/live service vs. 4mil users of "low" revenue desktop (incl Mac), so desktop has 10% of the total Turbotax user base for only 5% of the total Turbotax revenue. Turbotax revenue overall is expected to grow 8% in 2026 while desktop is declining 5%. etc.
They're also cutting bait on ItsDeductible which only had 100k users, and the Desktop Basic edition.
Clearly they're ok losing hundreds of thousands of users out of a base of 40mil if revenues are growing everywhere else. For most users who will inevitably be on Win 11 a year from now, it's a choice whether to deal with it in the next few months and keep tax process intact, or spend time changing tax process and then have to upgrade 6 months later anyway.
https://ttlc.intuit.com/community/articles/community-news-announcements/turbotax-windows-10-desktop-...
https://investors.intuit.com/news-events/press-releases/detail/1266/intuit-reports-strong-fourth-qua...
