As an engineer, I see this differently. A "language" is not simply (or always) syntax. Generally speaking, any API is already a language, and it's normal to use several APIs in one application; I'd even say, the more the merrier. Further, it is OK for an API to be represented as a DSL (domain-specific language) with a syntax of its own, so it's all good.
I also have an argument against the "too many languages" point: What's happening in the modern web is that HTML, CSS, and JS are slowly combining. A lot of projects are moving towards TSX components (Typescript and React, Vue, Svelte, etc.) with Tailwind CSS. So: Typing, layout, scripting, and styling all in one cohesive package that can easily be abstracted into components or classes.
I think eventually there will be a singularity of sorts where we have a standard toolkit/language.
From my own experience building websites and native apps, I can move around in web tech like a god damn ninja but I hate electron. I hate the inefficiency of using a browser for the UI. Qt and Gtk feel clunky and limited compared to web, but are native. But now there's Tauri, and I think it's a large step in the right direction.
HTML and CSS are not the answer. If anything, you should be scared off by the fact that webpages require at least three languages to implement anything useful (HTML, CSS, and JS), and that doesn't count whatever you could use for a backend (PHP? I'm not a web developer, so I don't know what the cool kids use, other than maybe Node.js.)
In my book, the fewer langauges you use, the better: I will even extend this to Qt and QML (and it should be pointed out that I am passionate about using Qt and QML!). Multiple languages necessitate (often fragile) bridges to work together; plus, they take much more time and effort to learn. If you could learn one language and use it to make an app, wouldn't you jump at that instead of learning 3 or 4 languages before you could make an app?
Others have already added some great comments about the wisdom (or rather the lack thereof) of integrating a web browser into the OS. Myself? I don't wish anybody a future of bloated webapps for everything.