They never got it, the current Teams app was never actually cross-platform. It has wildly different features depending on platform (browser, "native", OS). Funnily if you switch your user agent you get all features even on Linux (clearly the afterthought) though.
Software developers who actually know what they're doing and ignore fashion aren't as exciting to hire, I guess.
Instead, you leverage what you already have - any modern product is already going to have a web interface. The idea of packaging that interface into a self-contained desktop application with little to no additional effort is just too appealing. Sure, everybody else screws it up when attempting this route, and performance becomes a huge problem, but surely your team will do it right. And besides, webdevs are a dime a dozen compared to C++ guys (and fluent on two or three platforms? Good luck. You’ll pay through the nose the get them and more to keep them.)
Developers that know how to make native desktop apps well are a dying breed