Because, wonderful as Termux is, it has a very nonstandard filesystem layout, so installation scripts for something like Anaconda will not run without extensive modifications. And Termux has no access to /proc, /dev etc., so lots of utilities fail. Since Terminal provides a full Linux VM, all programs that will run on Linux just work as expected.

Termux can access the full file system if you have root access, which is how I play around with it; however, running a VM is a safer and easier route, especially as smartphone manufacturers are making it tougher to root the device you own.

I haven't noticed anything like that. Some more obscure tools have trouble with the file system but that happens in ordinary Linux too. Though I have no experience with Anaconda specifically so you likely know better whether it'll need adaptations to work under Termux.

I run htop just fine on my handhelds and I'm pretty sure it sources directly from /proc, /sys or something.