Tesla's capex spending is lower than their depreciation, meaning they're not investing enough to maintain their existing production lines. There is no way they will be rolling out any new models any time soon.
Additionally the MS and MX interiors are starting to get a bit dated compared to the ultra-sleek Model 3’s interior - the MS’s interior design is still fundamentally unchanged since 2012. They did upgrade the infotainment system in early 2018 though, but that’s invisible to users who don’t notice smoother framerates.